| Abstract
| - Cytokinesis is the process by which one cell divides into two. Key in the cytokinetic mechanismof Schizosaccharomyces pombe is the contractile ring myosin, which consists of two heavy chains (Myo2p),two essential light chains (Cdc4p), and two regulatory light chains (Rlc1p). Cdc4p is a dumbbell-shapedEF-hand protein composed of N- and C-terminal domains separated by a flexible linker. The propertiesof these two domains are of particular interest because each is hypothesized to have independent functionsin binding different components of the cytokinesis machinery. To help define these properties, we usedNMR spectroscopy to compare the structure, stability, and dynamics of the isolated N- and C-terminaldomains with one another and with native Cdc4p. On the basis of invariant chemical shifts, the N-domainretains the same structure in isolation as in the context of the full-length Cdc4p, whereas the C-domainappears markedly perturbed. This perturbation results from intramolecular binding of the residual linkersequence at the N-terminus of the C-domain in a mode similar to that used by native Cdc4p to associatewith target polypeptide sequences. NMR relaxation, thermal denaturation, and amide hydrogen exchangeexperiments also indicate that the C-domain is less stable and more dynamic than the N-domain, both inisolation and in the full-length protein. We hypothesize that these properties reflect a conformationalplasticity of the C-domain, which may allow Cdc4p to interact with several regulatory or contractile ringproteins necessary for cytokinesis.
|
