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    Proceedings of the Indian Academy of Sciences

  • 中文名称: 印度科学院院刊
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  • ISSN: 0253-4134
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  • 机译 I型胶原N端肽的二级结构已通过傅里叶变换红外光谱和分子建模证明
    摘要:The amino-telopeptides of type I collagen have been implicated to have a crucial role in the events of fibril formation. The sequences have been highly conserved in a variety of species. Several proposals have been presented to correlate the sequence with structure and role in fibri1 formation, but no definite information on telopeptide structure has been deduced. The infrared spectrum of the amide I band, due almost entirely to the C=O stretch vibration of peptide carbonyls, has been a most useful probe for determining the secondary structures of proteins in solution. In the present study, the secondary structure of a synthetic rat alpha 1 (I) amino-telopeptide has been investigated in aqueous solution by Fourier transform infrared spectroscopy (FTIRS) using a 9-pass internal reflectance ZnSe prism cell. Conformational changes were monitored as the aqueous solution was heated from 4 to 50 deg.C by observing changes in the freauency position. To support these experimental data the telopeptide region was modeled using BIOSYM/MSI software on a Silicon Graphics R-4000, X/Z graphics workstation. The proposed telopeptide structure was energy minimized using DISCOVER CVFF repetitive build and minimize process to reduce steric hindrance and maximize H- bonding. The potential energy surface was quite low and the conformation was stabilized by only 3 H-bonds. This model suggests a telopeptidc structure that can be induced to assume a conformation favorable for binding during its interchain interaction at the collagen helix cross-link (N-telopeptide) receptor domain around collagen
  • 机译 层粘连蛋白
    • 作者:HYNDA K KLEINMAN;
    • 刊名:Proceedings of the Indian Academy of Sciences
    • 1999年第1期
    摘要:The laminins are a family of trimeric basement membrane glycoproteins containing an alpha, beta and gamma chain. At least eleven family members have been described and others are likely to exist, many in tissue-specific locations. Five alpha, four beta and three gamma chains have been described further suggesting additional isoforms. Laminins are very biologically active with laminin-l (composed ofα|β|γ| chains) being the most studied. Laminin-l increases cell adhesion, migration, growth, differentiation, neurite outgrowth, protease production, and malignancy. The response of the cell is dependent on the cell type. A number of active sites on laminin including cryptic domains have been defined using protease-derived fragments, recombinant material and synthetic peptides. Various diseases involving mutations, deletions and autoantibodies to laminins have been identified demonstrating the important functions of this family of molecules in both development and disease. These studies demonstrate that the structural diversity of the laminins allows for many highly specialized functions .
  • 机译 前胶原基因的调节。从力量到因素
    摘要:Collagens are the most abundant vertebrate proteins. Their primary role is to provide a supportive scaffolding to which cells attach but other actions in cell communication and cell function are now recognized. The work of pioneers of collagen researeh, of whom G N Ramachandran is a giant, have provided us with a detailed understanding of collagens' structure and function. In many of the inherited disorders (i.e., osteogenesis imperfecta) specific molecular lesions have been identified in collagen genes but in the common diseases, such as fibrotic disorders or theumatoid arthritis, it is an imbalance in the rates of synthesis and breakdown which are critical. In vivo studies have shown that collagen turnover occurs at rapid rates in body tissues and that fibroblasts are dynamic cells actively synthesizing and degrading collagens. These cells are central to normal wound repair and the pathogenesis of fibrotic diseases. Theyorganise and respond to their extracellular milieu and produce cytokines which exert autocrine and paracrine effects. They react to a variety of stimuli, including feedback from procollagen breakdown products, mechanical forces and polypeptide mediators. Mediators which regulate procollagen tumover, include the TGFP family of homodimeric peptides which act via partially described signaling systems involving G-protein linked pathways. Elements of the coagulation cascade, including the serine protease thrombin, also promote collagen production and it is likely that these agents are part of a primitive system of haemostasis and tissue repair. For example, thr
  • 机译 胶原三聚体组装的机理
    摘要:It is generally accepted that the folding of collagen triple helical domains occur from the C-terminus toward the N-terminus by a "zipper" mecha- nism. The regions at the C-terminus of the triple helices must therefore play a critical role in the processes of chain recognition and assembly to get the proper stoichiometries and of chain registration to align the chains for the folding of the triple helix. Examination of these regions reveals a broad diversity of structures and suggests that different mechanisms of assembly are used in the various collagen and collagen-like molecules. We review here three different mechanisms that have recently come to light. The collectins, a group of serum proteins contain- ing collagen-like triple helical domains, are assembled through hydrophobic interactions in a triple a helix. Collagens Vlll and X, CIq and several related proteins contain homologous C-terminal domains that are characterized by a beta-pleated sheet structure. They assemble through very strong hydrophobic interactions that probably involve an ``aromatic zipper''. Collagens IX, Xll and XIV fibril associated collagen with interrupted triple helices (FACITs), are assembled by a mechanism in which both the C-terminal triple helix and a very short cysteine-containing sequence are involved.
  • 机译 马特拉金属蛋白酶及其抑制剂在肿瘤侵袭和转移中的作用
    摘要:Therecent progress in matrix metalloproteinases (MMPs) researeh has opened up many cellular targets in a variety of diseases. We have discussed some of the interesting and newly described roles of MMPs in modulating metastatic phenotypo in malignancies. This information suggests a more specific and exclusive role of MMPs as important regulatorr of tumorcell invasion and metastasis. A great deal of room exists for redefining our current understanding of the MMPs system, the more we understand about how MMPs act, the better we will understand the pathobiology of metastasis. Researeh in the regulation of MMPs and the potential use of MMPs for therapoutic interventions in metastasis continues to expand. The future of therapy involving inhibitors of MMPs as a part of the armamentarium against human neoplasm should be viewed with cautious optimism. This therapeutic approach is beginning to find a place in our understanding of metastatic tumors, but with perhaps few exceptions should still be considered experimental. This area of research now needs more biological knowledge and imagination on the part of investigators to make future achievements possible.
  • 机译 海洋无脊椎动物胶原蛋白:某些海洋甲壳类和软体动物组织中普遍存在V型和XI型胶原蛋白
    摘要:While the invertebrates constitute almost 95 of the animal kingdom, our knowledge on their extracellular matrices, particularly on collagen, is very scanty. Our group has been studying the collagen polymorphism in some marine invertebrate tissues with focus on structure-function relationships and molecular evolution. We have established methods to purify unique collagen molecules from some rare tissues of crustaceans and molluscs. Some of these include the intramuscular tissues of the crostaceans and the cartilage and comea of molluscs. The biochemical parameters in these tissues relating to collagen content, solubility and carbohydrate composition have been determined. The chain composition of these collagens were deduced by SDS-PAGE. We have analyzed the amino acid compositions of these collagens and that of isolated single alpha chains. The physicochemical properties and ultrastmctural charactetistics of some of these collagens were also studied. The results indicate that the principal component of crustacean muscle is a type V like homotrimer and that of molluscan cartilage and cornea is a unique heteromeric collagen resembling vertebrate type V and XI collagens. These collagens were invariably highly crosslinked, stabilized largely by bound cathohydrates and had significantly high denaturation temperatures. While the crustacean type V collagen formed regularly banded fibrils, the V/XI like collagen of molluscan cartilage lacked periodicity in fibril stmcture. We correlate the significance of our key observations to the possible functional consequence as well as evolut
  • 机译 金属蛋白酶组织抑制剂的表达及其生物学意义
    摘要:Matrix metalloproteinases (MMPs) are a family of zinc- and calcium- dependent proteases that are involved in degrading extracellular matrix (ECM). Tissue inhibitors of metalloproteinases (TIMPs) are naturally occutring proteins that inhibit MMP activity by binding noncovalently with the active forms of MMPs at molar equivalence. Of the four TIMPs characterized so far, TIMP- I and TIMP-2 participate in the inhibition of tumor growth, invasion, and metastasis. They also promote growth, inhibit angiogenesis, and modulate cell morphology. TIMP-3 is unique among the TIMPs in being a component of the ECM itself and in suppressing tumor cell growth. TIMP-4, the most recently discovered TIMP, has its gene allocated to human chromosome 3p25 and is perhaps the most tissue-specific of the TIMPs being expressed largely in the heart. Synthetic low-molecular-weight MMP inhibitors with a hydroxamate structure that mimics collagen have reduced the tumor burden and altered the growth of primary tumors in animal models. Understanding the biological significance of ThMPs and their involvement in tumorigenicity will be valuable for the development of effective novel therapeutic strategies for controlling tumor growth and metastasis. This chapter provides a brief review of the four TIMPs characterized thus far, focuses on their roles in tumorigenesis and angiogenesis and concludes with a brief look at the use of synthetic MMP inhibitors in cancer treatment.
  • 机译 新型三螺旋胶原蛋白模拟结构的设计,合成和构象
    摘要:We have synthesized collagen-like monodisperse structures. A series of single chain Ac-(Gly-pro-Hyp).-NHz where n = l , 3, 5, 6, 9 and template-assembled KTA-[Gly-(Gly-pro-Hyp)n-NH2}3 analogs (n = l, 3, 5, 6), where KTA is the Kemp triacid (cis- l,3,5-trimethyl cyclohexane-l,3,5-tricarboxylic acid), were assessed for triple helicity by CD, thermal denaturation and NMR spectroscopy. The KTA-based template induces a significant gain in free energy and reduces the critical chain length for triple helix formation over the acyl terminated single chain structures. Our approach also includes the incorporation of the peptoid residue N-isobutylglycine into the design for novel collagen-like sequences. We have synthesized and characterized acetylated single chain and template-assembled analogs composed of Glypro-Nleu and Gly-Nleu-Pro sequences. The achiral trimeric unit Gly-Nleu-Nleu was included as a guest sequence in a host structure such as Ac-(Glypro-Hyp)3-(Gly-Nleu- Nleu)3-(Gly-pro-Hyp)3-NH2 which retains triple helicity. A series of guest-host collagen mimetics composed of Gly-Nleu-Pro sequences as the host were synthesized and assessed for triple helicity. Guest sequences include Gly-Nleu-Nleu and Gly Nx-pro units, where Nx is the guest peptoid residue with alkyl and aralkyl side chains. We have continued to investigate functionalized template motifs and sequence variations. We are examining the effects of functionalization and sequence variation on triple helical stabilities and molecular properties in order to design novel collagen- based biomaterials .
  • 机译 胶原蛋白和胶原蛋白-糖胺聚糖基质作为生长因子的载体
    摘要:Tissue engineering is an emerging interdisciplinary field that applies the principles of engineeting to the life sciences, with the aim of developing biological substitutes that restore, maintain or improve tissue function. In this process, extracellular matrix, cells and regulatory signals are important in guiding, modulating and facilitating regenerative events. Cellular activities are regulated by a large number of polypeptides which behave as growth modulating factors. Such growth factorr can either stimulate or inhibit cell division, differentiation, migration or expression. The effects of such factorr are cell type-dependent and can vary with the frequency and way of administration. As we increase our understanding of growth factor functions and their clinical applications, the need for useful pharmaceutical forms becomes more apparent. Growth factor targeting to responsive cells and maintenance of adequate tissue levels becomes essential, particularly in view of their sometimes opposite effects on various cells and the dose dependence of their response. The extracellular matrix provides a scaffold for cell growth, differentiation and may help to eventually regenerate tissues. Since collagen is a major constituent of extracellular matrices and connective tissues, its use in designing a synthetic matrix becomes of special interest. .When growth factors contain collagen-binding domains, they can be targeted to collagen matrices, their activities localized, and together with the collagen matrix, synergistically affect the biological activities of cells. Therefore, collag
  • 机译 人透明质酸酶定位到候选肿瘤抑制物
    摘要:Eukaryotic hyaluronidases are widely distributed, but until recently the only vertebrate enzyme to be cloned was the sperm-specific enzyme, PH20. We have now purified the hyaluronidase of human plasma. The identical enzyme, as well as a second proteolytically processed form, is present in urine. Amino acid sequence of the purified hyaluronidase matched a cDNA in the human Expressed Sequence Tag database which, in combination with 5'-RACE-PCR, was used to clone the gene. termed HYALI, coding for a protein of 435 amino acids. HYALI is identical to an uncharacterized gene positionally cloned by others at chromosome 3p21.3 that is homozygously deleted in several small cell lung careinoma cell lines. We have also identified two additional paralogous hyaluronidase-like genes flanking HYAL1 on chromosome 3p21.3 termed HYAL2 and HYAL3. We are evaluating the candidacy of these two genes as potential tumor suppressors. The mouse hyaluronidase gene, by convention termed Hyall, was also cloned and expressed and found to be 73 identical to the human enzyme. In mouse, serum hyaluronidase polymorphism has previously been mapped to 60 cM from the centromere of chromosome 9, which corresponds to a cytogenetic location of gFI-F2, a region syntenic to the human 3pZ1.3. Mice with alleles of Hyall producing higher levels of plasma hyaluronidase have greater resistance to transplanted tumor growth. products of these candidate tumor suppressor genes are being evaluated as potential anticancer agents.
  • 机译 基底膜中IV型胶原蛋白网络的链组成
    摘要:Type IV collagen, the major component of basement membranes (BM), is a family of six very similar chains. This allows for many kinds (isoforms) of triple helical protomers. The protomers self-assemble into network-like supramolecular stroctures by dimerization through C-terminal (NCI) domains (resulting in six chains forming an NCI hexamer, and tetramerization through the protomer N-terminal domain. Studies on the networks of seminiferous tubule BM (STBM) involved affinity chromatography to fractionate NCI hexamers excised by collagenase digestion. Three major hexamer populations were obtained that contained alpha 1 (IV) and alpha 2(IV) chains, alpha 1 (IV) - alpha 6(IV) chains, and alpha 3(IV)-alpha 6(IV) chains, respectively, which indicated three major separate type IV collagen networks in STBM. To study glomemlar BM, we used selective proteolysis to separate large fragments of type IV collagen. These contained type IV collagen chains cross-linked between NCI domains, and al(IV) through as(IV) chains cross-linked between NCI domains as well between triple helices. The latter set of fragments contained a subset of disulfide- linked alph 3(IV), alpha 4(IV) and alpha 5(IV) chains. The existence of networks containing alpha3 (IV), alpha 4(IV) and alpha 5(IV) chains suggests a molecular basis for mutations in the gene encoding the alpha 5(IV) chain cansing defective assembly of not only alpha 5(IV) chains, but also alpha3(IV) and alpha 4(IV) chains in the GBM of patients with Alport syndrome. A significant result of these studies is that GBM contains three major type IV colla
  • 机译 胶原蛋白的7/2螺旋模型-来自模型肽的证据
    摘要:After about fifty years since the prediction of a triple-helical structure, there are still two models for collagen with different helical symmetry. One is the Rich and Crick model in which three strands form a left-handed 10/3-helix with an axial repeat of 28.6A. The other is the Okuyama model in which three strands form a left- handed 7/2-helix with an axial repeat of 20A. High-resolution structures of collagen model peptides (Pro-Pro-Gly)10 and (Pro-Hyp-Gly)10 strongly support the latter model. The comparison of water molecules found in these strutures, together with the water bridges involving the hydroxyl group of Hyp, indicated that water molecules do not contribute to the extra stability of the triple-helix as has been considered for many years. This observation agreed well with a recent finding that the extra stability of collagen with Hyp at the Y-position is due to the inductive effects rather than water bridges involving hydroxyl groups .
  • 机译 I型原胶原异源三聚体装配与前α1(I)和前α2(I)-羧基肽原的结构细微差别有关
    摘要:The assembly of the type I procollagen heterotrimer is initiated by an interaction between the carboxyl propeptides, with triple helix folding proceeding in the C -> N direction. The pro-alpha 1(I)-C-propeptides can interact with self to form the homotrimer or with pro-alpha 2(I)-C-propeptide to establish the heterotrimer. The two propeptides are similar in length and have about 65 identity in sequence. Nevertheless, we proposed that differences in interaction between propeptides might account for the in vivo selection of heterotrimer formation rather than homotrimer formation. To test this hypothesis we have determined the probable structures of.the human C-propeptides by molecular modeling and energy minimization using Molecular Simulations insight, Discover 95.0/3.0, and Biopolymer programs. The propeptide structures were constrained with the two known intrachain disulfide bonds in each case. The two structures were globally similar, with three distinct structural domains (G-I, L, G-II) in each case. A few crucial Pro residues and other sequence differences, however, produced different structures in each domain. The different interaction profiles of the three domains may be of crucial importance for heterotrimer selection
  • 机译 再谈胶原蛋白的热变性
    摘要:We have recently re-examined the characteristic sharp denaturation temperature of the collagen molecule and fibre. It has been generally accepted for many years that denaturation is an equilibrium process involving the rupture of hydrogen bonds. We have now proposed that the process is an irreversible rate process, in which uncoupling of the alpha-chains initially occurs in a thermally labile domain devoid of hydroxyproline. The domain is located near the C-terminal and following alignment of the molecules in the quarter-stagger-end-overlap arrangement is located in the gap region of the fibre. The domain appears to be conserved in type I of several animal species, and is present in types II and III. Collagen molecules that co-polymerise to form fibres, types V and XI, do not possess this labile domain. Ramachandran proposed that stabilisation of the triple helix occurred through hydrogen-bonded water-bridges involving the hydroxyl group of hydroxyproline. Recent studies have been equivocal, some questioning the role of water bridges and of hydroxyproline, whilst recent detailed X-ray studies of collagen-like peptides demonstrate the presence of a stabilising sheath of hydrogen-bonded water. Our findings support the proposal of hydrogen-bonded water-bridges stabilising the triple helix .
  • 机译 胶原蛋白成熟和老化的机制和后果
    摘要:The stabilisation of collagen fibres during development and through growth to maturation is now fairly well understood. It is a carefully controlled enzymic process which produces intermolecular cross-links at specific locations. In marked contrast, the changes in the physical properties that occur towards old age are stochastic and involve oxidative reactions that result in the formation of glucose mediated cross-links. This excessive and random cross-linking leads to a devastating loss of tissue functionality and deterioration of vital organs. In addition, specific residues involved in cell-matrix interactions may become modified. This can affect the expression of cells and lead to the formation of an inappropriate collagen matrix during its slower tumover in old age. This is exemplified in the ubiquitous disorders osteoporosis and osteoarthritis, age-related diseases in which we have noted gene regulated changes in the collagen deposited and also post-translational changes such as over-hydroxylation of lysine residues. Both of these effects can have a profound deleterious effect on the function of the matrix tissue.
  • 机译 马德拉斯族和胶原蛋白的结构
    摘要:The genesis of the collagen structure proposed by the Madras Group is briefly outlined. Recent crystal structure data on collagen-like peptides vindicate (i) the original proposal of Ramachandran and Kartha, namely, that the structure of collagen is a triple helical coiled-coil one , maximisation of hydrogen bonds directly or indirectly with water molecules, including C'-H. . .O hydrogen bonds
  • 机译 VI型胶原微纤维的STEM质谱图:对链组成和选择性剪接的影响
    摘要:Type VI collagen is a major structural interactive extracellular matrix macromolecule which forms double-beaded microfibrils in the extracellular space. These microfibrils can be isolated in native form from collagenase digest of skin fibroblast cell layers by chromatography on Sepharose CL-2B. Scanning transmission electron microscope (STEM) mass mapping showed a periodicity of 104 nm and a mass/bead of 1500 kDa. In addition, there was an uneven mass distribution along the bead. Microflbrils arise by end-to-end aggregation of tetramers which should produce microfibrils with bead mass of ≈ 2000 kDa and homogeneous mass distribution across the bead. Reduction in the mass across the bead implies either altered chain composition, alternative splicing or proteolytic degradation. The pattern of splicing of type VI chains in human tissues and their biological implications are poorly defined. In this study, we have examined the abundance of alternatively spliced forms of the alpha 2(VI) and a3(VI) chains in human skin fibroblasts. Both alpha2C2 and alpha2 C2a variants, but not the alpha2C2a' form, were expressed in these although the alpha2C2 form appeared more abundant. The alpha3(VI) N7 domain was frequently spliced out of transcripts present in skin fibroblasts, whereas the a3(VI) Ng domain was always present. No consistent pattern of splicing was observed and splicing is unlikely to account for the reduced mass observed in type VI collagen microfibrils.
  • 机译 Procollagn C蛋白酶及其增强蛋白可调节胶原纤维的形成和基质沉积
    • 作者:EFRAT KESSLER;
    • 刊名:Proceedings of the Indian Academy of Sciences
    • 1999年第1期
    摘要:Procollagen C-proteinase (PCP) and its enhancer protein (PCPE) are key to collagen fibril-assembly and extracellular matrix formation. PCP cleaves the carboxyl-propeptides of procollagens typos I, II, and lll and this initiates the self assembly of collagen fibrils. PCP can also process pro-lysyl oxidase and laminin 5, and it may cleave the type V procollagen N-propeptides. Procollagen processing by PCP is stimulated by PCPE, a glycoprotein that binds to the C-propeptide of type I procollagen through its N-terminal CUB domains. PCPE is also required for normal cell growth and morphology. Two distinct forms of PCP were isolated from mouse and chick sources. These were recently identified as altematively spliced products of the gene coding for bone morphogenetic protein-l (BMP-l), a member of a family of Zn-dependent astacin-like metalloendopeptidases implicated in tissue patteming and development. Typically, these are multidomain proteases that, in addition to their catalytic domain, contain a number of EGF-like and CUB protein-protein interaction domains. Recent evidence suggests that PCP/BMP-l related proteases can activate TGFp-like growth factors. There is also evidence for additional altematively spliced PCP variants. Thus, PCPs may have important biological functions in addition to their role in collagen fibril assembly.
  • 机译 I型胶原生物合成调控的分子机制
    摘要:Type I collagen is a heterotrimeric protein composed of two α(I) and one α2(I) polypeptide chains, each encoded by a unique gene. Both collagen genes are coordinately regulated in response to a variety of endogenous and exogenous stimuli. Collagen genes are mainly regulated by transcriptional mechanisms, although post- transcriptional regulatory mechanisms have occasionally been documented. To understand the molecular basis of transcriptional control, we have been studying the cis-regulatory sequence motifs of human pro αl(I) collagen gene and trans-acting factors with which these elements interact. The major elements include TATA and CCAAT boxes, Ap-l , Ap-2, NF-I and Spl , and a unique TGF beta l -activating element. Transcription factor Spl is obligatory for the activation of the Pro αl(I) promoter since it failed to be activated in Drosophila SL2 cells that lack Spl. Of the six putative Spl motifs in the Pro αl(I) collagen promoter and the first intron, the most proximal Spl element located at -87`to -82 bp was sufficient for its Spl -dependent activation. Additional cis-acting motifs in the intron of the Pro αl (I) gene, including an Ap-l site, participated in its regulation by TGF beta l and okadaic acid. Thus, activation of Pro α 1(I) promoter involves combinatorial actions of multiple ubiquitous and unique cis-regulatory elements. -
  • 机译 基质金属蛋白酶:调节和生物学功能
    摘要:Remodeling of the extracellular matrix occurs during many physiological and pathological conditions. The matrix metalloproteinases (MMPs) are a family of zinc-dependent proteases that are responsible for the proteolytic degradation of number of extracellular matrix (ECM) components. Regulation of MMP activity both at transcriptional and translational levels modulates the degradation of ECM components. Although most MMPs have similar regulatocy mechanisms, certain MMPs have unique mechanims of activation at the cell surface. Understanding the processes that regulate the expression of MMPs is important since an imbalance between MMPs and their natural inhibitors, tissue inhibitors of metalloproteinses, leads to a pathological situation such as cancer. In this review, we will briefly discuss various MMPs, their structure, regulation and function.
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