1、生物膜和细胞间生物膜和细胞间信息传递信息传递航海医学研究所航海医学研究所 朱朱 俐俐 2006.122006.12概述概述生物膜的组成和特点生物膜的组成和特点细胞的内膜系统细胞的内膜系统一一.概概 述述生物膜生物膜（Biological Membrane）是生物是生物体在漫长的进化过程中逐渐形成的，使细胞有体在漫长的进化过程中逐渐形成的，使细胞有了相对稳定的内环境。了相对稳定的内环境。包括：包括：细胞外层的质膜细胞外层的质膜 细胞器的膜细胞器的膜 核膜核膜 质膜使细胞成为生命活动的基本单位。质膜使细胞成为生命活动的基本单位。内膜系统使分隔开的各个细胞器具有独内膜系统使分隔开的各个细胞器具有独特
2、的功能。特的功能。本身参与多种生物反应过程。本身参与多种生物反应过程。基本功能：基本功能：与生命科学中许多基本问题都有密切关系，如细胞起源、遗与生命科学中许多基本问题都有密切关系，如细胞起源、遗传信息传递、生物能量转换、物质运转、激素作用、神经传导、细传信息传递、生物能量转换、物质运转、激素作用、神经传导、细胞免疫、细胞识别、细胞分化和增殖等。胞免疫、细胞识别、细胞分化和增殖等。生物膜的结构与功能的研究是细胞生物学、分子生物学、生生物膜的结构与功能的研究是细胞生物学、分子生物学、生物物理学、医学、仿生学等许多领域的热点。物物理学、医学、仿生学等许多领域的热点。Three views of a
3、cell membrane.(A)An electron micrograph of a plasma membrane(of a human red blood cell)seen in cross section.(B and C)These drawings show two-dimensional and three-dimensional views of a cell membrane.(A,courtesy of Daniel S.Friend.)The lipid molecules are arranged as a continuous double layer about
4、 5 nm thick.二二.生物膜的组成和特点生物膜的组成和特点 由由蛋白质、脂质和糖蛋白质、脂质和糖组成。不同类型的组成。不同类型的生物膜其脂质与蛋白质所占的比例不同。生物膜其脂质与蛋白质所占的比例不同。膜蛋白质膜蛋白质约占约占30 一一40，多是糖蛋白、脂蛋白、或糖脂蛋白。，多是糖蛋白、脂蛋白、或糖脂蛋白。膜脂质膜脂质约占约占40一一50，为磷脂、糖脂及胆固醇。，为磷脂、糖脂及胆固醇。糖糖占占5，有糖蛋白，糖脂及糖脂蛋白，有糖蛋白，糖脂及糖脂蛋白生物膜化学组成之间的连接方式：生物膜化学组成之间的连接方式：膜蛋白与膜脂膜蛋白与膜脂之间为之间为非共价键非共价键连接，包连接，包括表在膜蛋白与膜
5、脂之间以离子键或氢键括表在膜蛋白与膜脂之间以离子键或氢键方式进行连接。内在膜蛋白由于分子表面方式进行连接。内在膜蛋白由于分子表面多为非极性氨基酸残基，疏水性较大，与多为非极性氨基酸残基，疏水性较大，与膜脂之间以疏水键方式进行连接。膜脂之间以疏水键方式进行连接。膜脂与糖膜脂与糖之间为之间为共价键共价键连接，包括磷脂分连接，包括磷脂分子中磷酸的子中磷酸的-OH或鞘磷脂分子中鞘氨酸的或鞘磷脂分子中鞘氨酸的-OH与糖的与糖的-OH，形成，形成O-糖苷键糖苷键方式进行连接。方式进行连接。膜蛋白与糖膜蛋白与糖之间为之间为共价键共价键连接，包括膜蛋连接，包括膜蛋白分子中的天门冬氨酰的氨基与糖的白分子中的天门
6、冬氨酰的氨基与糖的-OH形成形成N-糖苷键糖苷键方式，膜蛋白分子中的丝氨酸或苏氨方式，膜蛋白分子中的丝氨酸或苏氨酸的酸的-OH与糖的与糖的O-糖苷键糖苷键方式进行连接。方式进行连接。Schematic diagram of typical membrane proteins in a biological membrane.The phospholipid bilayer,the basic structure of all cellular membranes,consists of two leaflets of phospholipid molecules whose fatty acy
7、l tails form the hydrophobic interior of the bilayer;their polar,hydrophilic head groups line both surfaces.Most integral proteins span the bilayer as shown;a few are tethered to one leaflet by a covalently attached lipid anchor group.Peripheral proteins are primarily associated with the membrane by
8、 specific protein-protein interactions.Oligosaccharides bind mainly to membrane proteins;however,some bind to lipids,forming glycolipids.：甘油磷脂及鞘磷脂：甘油磷脂及鞘磷脂糖脂：糖鞘氨脂及糖甘油脂糖脂：糖鞘氨脂及糖甘油脂胆固醇胆固醇:1.组成组成 (1)甘油磷脂（磷酸甘油酯）甘油磷脂（磷酸甘油酯）包括甘油骨架，两个脂包括甘油骨架，两个脂肪酸及磷酸化的醇。肪酸及磷酸化的醇。HOCHCH2OHCH2O H甘油甘油R2OCOCHCH2OCOR1CH2O P O H
9、OOHL-磷脂酸磷脂酸（一）、膜脂质的特点（一）、膜脂质的特点R2OCOCHCH2OCOR1CH2O P O CH2 CH2 N+(CH3)3OO-非极性部分（疏水尾）非极性部分（疏水尾）极性部分（极性头）极性部分（极性头）胆碱磷脂（磷脂酰胆碱磷脂（磷脂酰胆碱，卵磷脂）胆碱，卵磷脂）磷脂结构示意磷脂结构示意The effect of a double bond磷酸基分别与丝氨酸、乙醇胺、胆碱或肌醇结合即形成磷酸基分别与丝氨酸、乙醇胺、胆碱或肌醇结合即形成:丝氨酸磷脂丝氨酸磷脂(Phosphatidylserine PS)，又称，又称磷脂酰丝氨酸磷脂酰丝氨酸 乙醇胺磷脂乙醇胺磷脂(Phospha
10、tidylethanoamine PE)，磷脂酰乙醇胺磷脂酰乙醇胺 胆碱磷脂胆碱磷脂(Phosphatidylcholine PC)，磷脂酰胆碱磷脂酰胆碱 肌醇磷脂肌醇磷脂(phosphatidylinositol PI)，磷脂酰肌醇磷脂酰肌醇组成膜主要成分的组成膜主要成分的四种磷脂四种磷脂R2OCOCHCH2OCOR1CH2O P O CH2 C N+H3OO-HCOO-R2OCOCHCH2OCOR1CH2O P O CH2 CH2 N+H3OO-磷脂酰丝氨酸磷脂酰丝氨酸（PS）磷脂酰乙醇胺磷脂酰乙醇胺(PE)磷脂酰肌醇磷脂酰肌醇(2)鞘磷脂鞘磷脂(sphingomyelin,SM)不含甘油
11、，而代之以不含甘油，而代之以鞘氨醇鞘氨醇(C18)，鞘氨醇的鞘氨醇的C-1羟基，被磷酸胆碱化，长羟基，被磷酸胆碱化，长链的链的脂肪酸脂肪酸结合在鞘氨醇的结合在鞘氨醇的C-2位的氨基上。位的氨基上。磷酸鞘氨醇磷酸鞘氨醇（神经）鞘氨醇（神经）鞘氨醇葡萄糖脑苷脂葡萄糖脑苷脂油酸油酸磷脂酰胆碱磷脂酰胆碱（神经）鞘磷脂（神经）鞘磷脂固醇固醇（steroid）：质膜中的固醇，以）：质膜中的固醇，以胆固醇胆固醇(cholesterol)为主，胆固醇酯很少，主要起调节生为主，胆固醇酯很少，主要起调节生物膜中脂质的物理状态。物膜中脂质的物理状态。胆固醇的量与磷脂有一定比例，常胆固醇的量与磷脂有一定比例，常以测定
12、胆固醇磷脂比例来鉴定膜以测定胆固醇磷脂比例来鉴定膜是否有病变，此比值称是否有病变，此比值称cp比，各比，各种细胞膜的种细胞膜的cp值相差较多，约为值相差较多，约为0.030.1。(1)形成脂质双层结构形成脂质双层结构(2)膜磷脂的极性头部通过疏水力、静电引力和膜磷脂的极性头部通过疏水力、静电引力和氢键，对水有强烈的亲和力，因而排列在外，与氢键，对水有强烈的亲和力，因而排列在外，与外界外界(或胞浆或胞浆)水溶性环境相邻；其非极性区互相聚水溶性环境相邻；其非极性区互相聚集，尽量避免与水接触，所以排列在内部。集，尽量避免与水接触，所以排列在内部。两个分子磷脂的非极性区尾尾相联，决定了脂两个分子磷脂的
13、非极性区尾尾相联，决定了脂质双层的结构。质双层的结构。2.膜脂质的结构特点膜脂质的结构特点Figure 10-10.Four major phospholipids in mammalian plasma membranes.Note that different head groups are represented by different symbols in this figure and the next.All of the lipid molecules shown are derived from glycerol except for sphingomyelin,which
14、is derived from serine.Experimental formation of pure phospholipid bilayers.A preparation of biological membranes is treated with an organic solvent,such as a mixture of chloroform and methanol(3:1),which selectively solubilizes the phospholipids and cholesterol.Proteins and carbohydrates remain in
15、an insoluble residue.The solvent is removed by evaporation.If the lipids are mechanically dispersed in water,they spontaneously form a liposome,shown in cross-section,with an internal aqueous compartment.(Bottom right)A planar bilayer,also shown in cross-section,can form over a small hole in a parti
16、tion separating two aqueous phases;such bilayers are often termed“black lipid membranes”because of their appearance.(2)不对称性：不对称性：膜脂质双层两侧分布的不对称性决定于磷脂的头膜脂质双层两侧分布的不对称性决定于磷脂的头部，脂质双层部，脂质双层内侧内侧是两个含有氨基的磷脂是两个含有氨基的磷脂(PS、PE)，有较强的负电性有较强的负电性;PC及及SM在脂质双层的外侧。在脂质双层的外侧。内外两侧磷脂的脂肪酸也不完全相同，内外两侧磷脂的脂肪酸也不完全相同，PC及及SM多为饱和脂肪
17、酸，多为饱和脂肪酸，PS、PE含不饱和脂肪酸较多。含不饱和脂肪酸较多。Figure 10-11.The asymmetrical distribution of phospholipids and glycolipids in the lipid bilayer of human red blood cells.The symbols used for the phospholipids are those introduced in Figure 10-10.In addition,glycolipids are drawn with hexagonal polar head groups(
18、blue).Cholesterol(not shown)is thought to be distributed about equally in both monolayers.50%40%30%20%10%0 10%20%30%40%50%人红细胞膜中磷脂分布的不对称性人红细胞膜中磷脂分布的不对称性膜外侧膜外侧膜内侧膜内侧磷脂酰胆碱磷脂酰胆碱磷脂酰乙醇胺磷脂酰乙醇胺磷脂酰丝氨酸磷脂酰丝氨酸鞘磷脂鞘磷脂总磷脂总磷脂(3)膜脂质的运动膜脂质的运动:测定磷脂不同部位的运动速度及偏转的角度，测定磷脂不同部位的运动速度及偏转的角度，发现其极性头部运动较快，脂肪酸梁最慢。膜脂质发现其极性头部运动较快，
19、脂肪酸梁最慢。膜脂质运动方式有五种：运动方式有五种：脂肪酰链的旋转异构化运动脂肪酰链的旋转异构化运动 磷脂分子围绕其长轴的旋转运动磷脂分子围绕其长轴的旋转运动 磷脂侧向扩散运动磷脂侧向扩散运动 脂质分子在脂双层之间的翻转运动脂质分子在脂双层之间的翻转运动 脂肪酰链垂直于膜双分子层平面轴的振荡运动脂肪酰链垂直于膜双分子层平面轴的振荡运动 翻转(flip-flop)侧向移动摇动旋动膜脂质运动方式示意膜脂质运动方式示意(4)膜质脂的相变和分相：膜质脂的相变和分相：相变（相变（phase transition）和和分相分相是生物膜结构是生物膜结构的特征之一。在生理温度下，膜脂双层中一部分的特征之一。在
20、生理温度下，膜脂双层中一部分表现为流动态表现为流动态(液晶态液晶态)，另一部分表现为固态，另一部分表现为固态(结结晶态晶态)。因此，在膜平面上看，显示。因此，在膜平面上看，显示分相分相现象。现象。从液态变为晶态成为从液态变为晶态成为相变。相变。引起相变的温度称引起相变的温度称为为相变温度相变温度。磷脂的磷脂的相变相变与其与其成分和环境成分和环境有密切关系有密切关系:（1）脂肪酰链的）脂肪酰链的饱和度饱和度及及链的长短链的长短（愈短、愈不饱（愈短、愈不饱和，烃链愈不易靠紧，相变温度愈低）和，烃链愈不易靠紧，相变温度愈低）（2）胆固醇对流动性的影响（增加力学稳定；防止）胆固醇对流动性的影响（增加力
21、学稳定；防止低温引起的相变）低温引起的相变）（3）温度）温度Figure 10-7.Influence of cis-double bonds in hydrocarbon chains.The double bonds make it more difficult to pack the chains together and therefore make the lipid bilayer more difficult to freeze.Heat induces transition from a gel to a fluid over a temperature range of on
22、ly a few degrees.The fluid phase is favored by the presence of short fatty acyl chains and by a double bond in the chains;thus these structural features reduce the melting temperature of bilayers.Alternative forms of the phospholipid bilayer.生物膜所有的生物活性都由生物膜所有的生物活性都由蛋白质蛋白质来实现。功能来实现。功能越复杂，膜上所含蛋白质量就越大。
23、越复杂，膜上所含蛋白质量就越大。膜内的蛋白有单纯的蛋白，但更多的是糖蛋白。膜内的蛋白有单纯的蛋白，但更多的是糖蛋白。糖蛋白占膜蛋白中的比例大，结构复杂，功能多，糖蛋白占膜蛋白中的比例大，结构复杂，功能多，许多反应都是糖蛋白中糖链起着关键性的作用，它是许多反应都是糖蛋白中糖链起着关键性的作用，它是膜的门户，有人称它为膜的门户，有人称它为“天线天线”。（二）、膜蛋白的特点（二）、膜蛋白的特点 1、糖蛋白的结构：、糖蛋白的结构：糖与多肽的结合有两种类型：糖与多肽的结合有两种类型：N-糖苷型：糖苷型：葡萄糖与蛋白质的天门冬酰胺结合葡萄糖与蛋白质的天门冬酰胺结合 O-糖苷型：糖苷型：N-乙酰氨基半乳糖与
24、丝氨酸或苏氨酸结乙酰氨基半乳糖与丝氨酸或苏氨酸结合合2、膜蛋白在膜内的组装：、膜蛋白在膜内的组装：按蛋白质在膜内的部位分两类：按蛋白质在膜内的部位分两类：外在蛋白外在蛋白（外周蛋白）：脂双层的内、外表面，（外周蛋白）：脂双层的内、外表面，占占20-30%，主要在内表面，水溶性蛋白，通过温，主要在内表面，水溶性蛋白，通过温和的方法与膜分离。和的方法与膜分离。内在蛋白内在蛋白（固有蛋白）：镶嵌于脂双层内，占（固有蛋白）：镶嵌于脂双层内，占70-80%，膜生物功能的主要承担者，与膜结合紧，膜生物功能的主要承担者，与膜结合紧密，只能用去污剂使膜崩解。密，只能用去污剂使膜崩解。大多数固有蛋白分两大类：大
25、多数固有蛋白分两大类：通过一段小的疏水区域连接或定位于脂双层通过一段小的疏水区域连接或定位于脂双层膜上，其余部分伸展出膜的一侧或两侧。膜上，其余部分伸展出膜的一侧或两侧。类似于球形，大部分片段包埋于膜中，膜外类似于球形，大部分片段包埋于膜中，膜外侧仅暴露很小部分。侧仅暴露很小部分。Various ways in which membrane proteins associate with the lipid bilayer.(1)a single a helix,have a covalently attached fatty acid chain inserted in the cytoso
26、lic lipid monolayer.(2)as multiple a helices,(3)as a rolled-up b sheet(a b barrel).Some of these single-pass and multipass proteins have a covalently like(1).Other membrane proteins are exposed at only one side of the membrane.(4)Anchored to the cytosolic surface by an amphipathic a helix that parti
27、tions into the cytosolic monolayer of the lipid bilayer through the hydrophobic face of the helix.(5)Attached to the bilayer solely by a covalently attached lipid chain either a fatty acid chain or a prenyl group in the cytosolic monolayer(6)Via an oligosaccharide linker,to phosphatidylinositol in t
28、he noncytosolic monolayer.(7)(7,8)Many proteins are attached to the membrane only by noncovalent interactions with other membrane proteins.已分离提纯的膜蛋白有几百种之多，这些蛋白质在膜内组装已分离提纯的膜蛋白有几百种之多，这些蛋白质在膜内组装各不相同，大约可分为各不相同，大约可分为6种类型：种类型：形成通道形成通道特殊的固有蛋白脂锚定蛋白特殊的固有蛋白脂锚定蛋白（lipid-anchored proteins）脂锚定蛋白可与脂质分子形成共价键，而脂质分脂锚
29、定蛋白可与脂质分子形成共价键，而脂质分子的一部分位于膜双层中间，由此有效的把共价相连子的一部分位于膜双层中间，由此有效的把共价相连的蛋白质锚定在膜上，调节膜蛋白的活性。的蛋白质锚定在膜上，调节膜蛋白的活性。四种常见的连接方式：四种常见的连接方式：1、肉豆蔻酸的、肉豆蔻酸的酰胺键酰胺键锚定：锚定：cAMP依赖的蛋白激酶的催化亚依赖的蛋白激酶的催化亚基，基，G蛋白的蛋白的亚基等亚基等2、脂肪酸的、脂肪酸的硫酯键硫酯键锚定：锚定：G蛋白偶联的受体，一些病毒的表蛋白偶联的受体，一些病毒的表面糖蛋白面糖蛋白3、含异戊二烯基的、含异戊二烯基的硫醚键硫醚键锚定：锚定：p21ras蛋白，核膜层蛋白等蛋白，核膜
30、层蛋白等4、糖基、糖基磷脂酰肌醇磷脂酰肌醇锚定：如乙酰胆碱酯酶，甲状腺球蛋白等锚定：如乙酰胆碱酯酶，甲状腺球蛋白等Membrane protein attachment by a fatty acid chain or a prenyl group.(A)A fatty acid chain(myristic acid)is attached via an amide linkage to an N-terminal glycine.(B)A prenyl group(C)a myristyl anchor(D)a farnesyl anchor酰胺键酰胺键硫醚键硫醚键The covalent
31、 attachment of either type of lipid can help localize a water-soluble protein to a membrane after its synthesis in the cytosol.(A)A fatty acid chain(myristic acid)is attached via an amide linkage to an N-terminal glycine.(B)A prenyl group is attached via a thioether linkage to a cysteine residue tha
32、t is initially located four residues from the proteins C-terminus.After this prenylation,the terminal three amino acids are cleaved off,and the new C-terminus is methylated before insertion into the membrane.Palmitic acid,an 18 carbon saturated fatty acid,can also be attached to some proteins via th
33、ioester bonds formed with internal cysteine side chains.This modification is often reversible,allowing proteins to become recruited to membranes only when needed.(C)The structures of two lipid anchors are shown below:(D)(C)a myristyl anchor(a 14-carbon saturated fatty acid chain),(E)(D)a farnesyl an
34、chor(a 15-carbon unsaturated hydrocarbon chain).Only the a-carbon backbone of the polypeptide chain is shown,with the hydrophobic amino acids in green and yellow.The polypeptide segment shown is part of the bacterial photosynthetic reaction centerA segment of a transmembrane polypeptide chain crossi
35、ng the lipid bilayer as an a helix.(Based on data from J.Deisenhofer et al.,Nature 318:618 624,1985,and H.Michel et al.,EMBO J.5:1149 1158,1986.)Fig 22.A single-pass transmembrane protein.Note that the polypeptide chain traverses the lipid bilayer as a right-handed a helix and that the oligosacchari
36、de chains and disulfide bonds are all on the noncytosolic surface of the membrane.The sulfhydryl groups in the cytosolic domain of the protein do not normally form disulfide bonds because the reducing environment in the cytosol maintains these groups in their reduced(-SH)form.The detergent disrupts
37、the lipid bilayer and brings the proteins into solution as protein-lipid-detergent complexes.The phospholipids in the membrane are also solubilized by the detergent.Fig24.Solubilizing membrane proteins with a mild detergent Sodium dodecyl sulfate(SDS)is an anionic（阴离子）（阴离子）detergent,and Triton X-100
38、 is a nonionic detergent.The hydrophobic portion of each detergent is shown in green,and the hydrophilic portion is shown in blue.The bracketed portion of Triton X-100 is repeated about eight times.Fig 25.The structures of two commonly used detergents In this example,functional Na+-K+pump molecules
39、are purified and incorporated into phospholipid vesicles.The Na+-K+pump is an ion pump that is present in the plasma membrane of most animal cells;it uses the energy of ATP hydrolysis to pump Na+out of the cell and K+in.Fig26.The use of mild detergents for solubilizing,purifying,and reconstituting f
40、unctional membrane protein systemsFig31.The spectrin-based cytoskeleton on the cytosolic side of the human red blood cell membrane.(B,courtesy of T.Byers and D.Branton,Proc.Natl.Acad.Sci.USA 82:6153 6157,1985.National Academy of Sciences.)The structure is shown(A)schematically and(B)in an electron m
41、icrograph.The arrangement shown in the drawing has been deduced mainly from studies on the interactions of purified proteins in vitro.Spectrin dimers are linked together into a netlike meshwork by junctional complexes composed of short actin filaments(containing 13 actin monomers),band 4.1,adducin,a
42、nd a tropomyosin molecule that probably determines the length of the actin filaments.The cytoskeleton is linked to the membrane by the indirect binding of spectrin tetramers to some band 3 proteins via ankyrin molecules,as well as by the binding of band 4.1 proteins to both band 3 and glycophorin(no
43、t shown).The electron micrograph shows the cytoskeleton on the cytosolic side of a red blood cell membrane after fixation and negative staining.The spectrin meshwork has been purposely stretched out to allow the details of its structure to be seen.In a normal cell,the meshwork shown would be much mo
44、re crowded and occupy only about one-tenth of this area.Fig32.Converting a single-chain multipass protein into a two-chain multipass protein.(A)Proteolytic cleavage of one loop to create two fragments that stay together and function normally.(B)Expression of the same two fragments from separate gene
45、s gives rise to a similar protein that functions normally.(Adapted from H.Luecke et al.,Science 286:255 260,1999.)Fig37.The three-dimensional structure of a bacteriorhodopsin molecule.The polypeptide chain crosses the lipid bilayer seven times as a helices.The location of the retinal chromophore(pur
46、ple)and the probable pathway taken by protons during the light-activated pumping cycle are shown.The first and key step is the passing of a H+from the chromophore to the side chain of aspartic acid 85(red)that occurs upon absorption of a photon by the chromophore.Subsequently,other H+transfers utili
47、zing the hydrophilic amino acid side chains that line a path through the membrane complete the pumping cycle and return the enzyme to its starting state.Color code:glutamic acid(orange),aspartic acid(red),arginine(blue).Fig38.The three-dimensional structure of the photosynthetic reaction center of t
48、he bacterium Rhodopseudomonas viridis.(Adapted from a drawing by J.Richardson based on data from J.Deisenhofer,O.Epp,K.Miki,R.Huber,and H.Michel,Nature 318:618 624,1985.)The structure was determined by x-ray diffraction analysis of crystals of this transmembrane protein complex.The complex consists
49、of four subunits L,M,H,and a cytochrome.The L and M subunits form the core of the reaction center,and each contains five a helices that span the lipid bilayer.The locations of the various electron carrier coenzymes are shown in black.Note that the coenzymes are arranged in the spaces between the hel
50、ices.Special proteins inserted in cellular membranes create pores that permit the passage of molecules across them.The bacterial protein shown here uses the energy from light(photons)to activate the pumping of protons across the plasma membrane.(Adapted from H.Luecke et al.,Science 286:255 260,1999.
