Dynamic interaction between chaperone and its substrates

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SummaryChaperonin encapsulates unfolded proteins in the cis cavity and ensures safe folding without fear of aggregation. This process requires the energy of ATP hydrolysis. Currently prevailing model of chaperonin function assumes only a single rate-limiting step in whole catalytic cycle of chaperonin, that is, ATP hydrolysis that needs 8 sec. However, Yoshida and Funatsu〓s group have proposed that there are two rate limiting steps in the cycle, one 3 sec and the other 5 sec. This is based on the single molecule observation that GroES release, ADP release, and protein folding initiated by addition of ATP only start after a 3-sec lag phase. Kuwajima showed the conformational change occurred by the ATP binding rather than ATP hydrolysis. Tokuda〓 group have found a new factor, SecG, in SecA system. Similar to SecA, during protein translocation, SecG tumbles in the membrane. Kohno identified that ER stress sensor protein, IRE1-beta, is an RNase that cleaves 28SrRNA. Gotoh succeeded in expression of human beta-microglobulin in yeast cells and pointed out that disulfide bond is important in formation of amyloid fibers. Yoshida〓s group has established a real-time observation system that allows the growth of single amyloid fiber. The result showed that fiber grew predominantly unnidirectionally.