生物化學(xué)教學(xué)課件：§4 Protein function

1、liguofu 4 Protein Function 4.1 Oxygen-Binding Proteins 4.2 Muscle contraction 4.3 Conclusion What we really want to know is how proteins work. Let us learn from Oxygen-Binding Proteins and Muscle contraction. liguofu 4.1 Oxygen-Binding Proteins 1. Structure of Myoglobin and Hemoglobin 2. O2-binding

2、of Mb and Hb 3. Factors effect on the O2-binding of Hb 4. Hb Mutation decrease of the affinity of BPG liguofu Hb 在人體發(fā)育過程中的類型變化在人體發(fā)育過程中的類型變化 In embryo: 22 22 22 22 In fetus: Hb F (22) In adult： Hb A (22) Hb A2 (22) Hb F (22) liguofu 4.1 Oxygen-Binding Proteins 1. Structure of Myoglobin and Hemoglobin

3、 2. O2-binding of Mb and Hb 3. Factors effect on the O2-binding of Hb 4. Hb Mutation & disease liguofu Distribution of mutations in human hemoglobin GluVal Sickle cell anemia liguofu liguofu Sickle cell anemia is caused by a single amino acid replacement on the b b subunit: Glu6Val liguofuGluVal lig

4、uofu liguofu Electron micrograph of deoxy-Hb S fibers spilling out of a ruptured erythrocyte. The sickled cells are fragile. Their breakdown leads to an anemia that leaves the victim susceptible to infections and diseases. liguofu The elongated cells tend to block capillaries, causing inflammation a

5、nd considerable pain liguofu By By Linus PaulingLinus Pauling in 1949 in 1949. 1903 1987 Normal TraitPatient (Normal) (defective) liguofu Hb AS 雜合子個體具有明顯的雜合子個體具有明顯的 抗瘧疾（抗瘧疾（malaria）特征）特征 Hb AS 基因型基因型頻率頻率在非洲部分地區(qū)相當(dāng)高在非洲部分地區(qū)相當(dāng)高 Plasmodium (瘧原蟲）在紅細(xì)胞內(nèi)的代謝瘧原蟲）在紅細(xì)胞內(nèi)的代謝 導(dǎo)致導(dǎo)致pH下降，引起下降，引起 Bohr effect，出現(xiàn)更，出現(xiàn)更 多的

6、多的S型脫氧血紅蛋白（型脫氧血紅蛋白（deoxy-HbS），）， 聚集形成纖維沉淀聚集形成纖維沉淀, 導(dǎo)致紅細(xì)胞鐮刀化，導(dǎo)致紅細(xì)胞鐮刀化， 被脾臟清除。既被脾臟清除。既Hb AS 雜合子個體感染雜合子個體感染瘧瘧 原蟲的紅細(xì)胞易于被原蟲的紅細(xì)胞易于被脾臟脾臟清除。清除。 liguofu 4 Protein Function 4.1 Oxygen-Binding Proteins 4.2 Muscle contraction 4.3 Conclusion liguofu Muscle structure liguofu Muscle structure liguofu Muscle struct

7、ure liguofu Muscle contraction H band liguofu Muscle contraction liguofu 2.Actin molecules 3.Tropomyosin molecules 4.Troponin molecules Cross bridges (head groups of myosin molecules) Actin Tropomyosin Troponin 1. Myosin molecule head groups Split by papain Thin filament Thin filament Thick filament

8、 liguofu 1.Myosin (1) (Two heavy chain) (four) Mr = 540, 000 MrH = 220, 000 MrL = 20, 000 325 nm liguofu 1.Myosin (2) liguofu 1.Myosin (3)：S1 structure liguofu 1.Myosin (3)：S1 structure liguofu 2.G actin F actin (1) liguofu 2.G actin F actin (2) = Ca2+ or Mg2+ liguofu 2.G actin F actin (3) liguofu I

9、nteraction between myosin and F-actin liguofu Step 1 Step 2 The “power stroke” model of muscle contraction (ATP-consuming Motor) Two conformations of the cross-bridge were detected in insect muscle (1965) liguofu Step 3 Step 4 Step 1 liguofu Tropomyosin: lying along the groove in the F-actin helix.

10、Troponin: TnC, TnI, TnT TnC: the Ca2+binding subunit TnI: the inhibitory subunit TnT: the Tm-binding subunit Tm & Tn inhibit the binding of myosin heads to actin unless Ca2+ is about 10-5M. In resting muscle, Ca2+ is about 10-7M. The interaction between actin and myosin are regulated mainly by tropo

11、myosin and troponin. liguofu 3. Tropomyosin：coiled-coil liguofu 4. Troponin (1) TnC: red TnI: light blue TnC binding region: blue TnT: yellow Bound Ca2+: black RH: regulatory head IT arm: TnI-TnT arm liguofu Ca2 4. Troponin (2) C-TnI: C-terminal region of TnI C-TnT: C-terminal region of TnT TnIreg:

12、regulatory region of TnI :Regions where the structures are not well defined liguofu Animation: process of muscle contraction liguofu Ca2 approaches Troponin Ca2 activates Tn to expose binding site for Myosin head Mg2 approaches Mh Mh binds with Actin. Mg2 activates Mh causing release of Pi from ATP

13、leaving ADP and causing the Mh to contract Mg2and ADP released from Mh, ending its contraction Mh releases from Actin. Ca2 released from Tn, allowing it to cover binding site. Next cycle. liguofu 4 Protein Function 4.1 Oxygen-Binding Proteins 4.2 Muscle contraction 4.3 Conclusion liguofu 1. The interaction with other molecule (ligand) is reversible, and the dissociation constant kd indicates the interaction intensity. Hydrophobic groups liguo