Collagen triple-helix formation in all-trans chains proceeds by a nucleation/growth mechanism with a purely entropic barrier

被引:45
作者
Bachmann, A
Kiefhaber, T
Boudko, S
Engel, J
Bächinger, HP
机构
[1] Univ Basel, Bioctr, Dept Biophys Chem, CH-4056 Basel, Switzerland
[2] Oregon Hlth & Sci Univ, Dept Biochem & Mol Biol, Shriners Hosp Children, Res Ctr, Portland, OR 97239 USA
关键词
collagen folding; nucleation mechanism; double jump; activation energy;
D O I
10.1073/pnas.0505141102
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
Collagen consists of repetitive Gly-Xaa-Yaa tripepticle units with proline and hydroxyproline frequently found in the Xaa and Yaa position, respectively. This sequence motif allows the formation of a highly regular triple helix that is stabilized by steric (entropic) restrictions in the constituent polyproline-II-helices and backbone hydrogen bonds between the three strands. Concentration-dependent association reactions and slow prolyl isomerization steps have been identified as major rate-limiting processes during collagen folding. To gain information on the dynamics of triple-helix formation in the absence of these slow reactions, we performed stopped-flow double-jump experiments on cross-linked fragments derived from human type III collagen. This technique allowed us to measure concentration-independent folding kinetics starting from unfolded chains with all pepticle bonds in the trans conformation. The results show that triple-helix formation occurs with a rate constant of 113 +/- 20 s(-1) at 3.7 degrees C and is virtually independent of temperature, indicating a purely entropic barrier. Comparison of the effect of guaniclinium chloride on folding kinetics and stability reveals that the rate-limiting step is represented by bringing 10 consecutive tripepticle units (3.3 per strand) into a triple-helical conformation. The following addition of tripepticle units occurs on a much faster time scale and cannot be observed experimentally. These results support an entropy-controlled zipper-like nucleation/growth mechanism for collagen triple-helix formation.
引用
收藏
页码:13897 / 13902
页数:6
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