| Abstract |
The aim of the following thesis was the investigation of the intramolecular interactios of the SecA ATPase, the motor protein which together with the membrane protein SecY catalyze protein secretion in bacteria. SecA consists of two primary domains: the N-domain (70 KDa) hydrolyzes ATP and the C-domain (34 KDa) is needed for the binding and the insertion of the protein into the membrane. SecA catalyzes protein secretion during cycles of insertion and deinsertion from the membrane. It has been shown that the two primary domains create a physical complex by interacting with each other. This interaction is important not only from a structural point of view but also because it has functional significance. Using SecA proteins with mutations in their C-domain, a sequence was found between amino acyl residues 780-800 that is a regulator of the ATPase activity of the N-domain. More specifically it was shown that this sequence although not important for single cycles of binding and hydrolysis of ATP from soluble SecA, it represses multiple cycles of ATP interactions , through physical contact between the N- and C-domains. Furthermore, when SecA is bound to the membrane, the sequence 780-800 is important for both the membrane and the translocation ATPase activities. Finally the sequence 780-800 was shown to be important for the translocation of proteins both in vivo and in vitro. Previously it was established that SecA physically interacts with the SecY protein, through a part of the C-domain of SecA which encompasses the sequence 780-800. Taken together all these observations lead to the conclusion that this sequence is a mechanistic link that brings the SecA and the SecY proteins together. It is proposed that SecY, possibly acting in concert with the substrate, regulates the ATPase activity of SecA through the sequence 780-800, thereby inducing cyclic movements of SecA in the membrane during protein secretion .
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Ενδομοριακές επιδράσεις στη SecA πρωτεΐνη
