Is the Function of the cdc2 Kinase Subunit Proteins Tuned by Their Propensities To Oligomerize? Conformational States in Solution of the cdc2 Kinase Partners p13suc1 and p9cksphy

Abstract

The cdc2 kinase subunit (cks) proteins play an essential function in the control of mitosis through their molecular complexes with the cdc2 kinase. In this work, we characterize the conformational state(s) in solution of the cks proteins p13^suc1 from Schizosaccharomyces pombe and p9^cksphy from Physarum polycephalum. Monomers of p13^suc1 and p9^cksphy were found to be markedly nonglobular, presumably with a long, nonfolded C-terminal moiety. This was in contrast to the previously published structure of p13^suc1, derived from crystallographic studies on a zinc-promoted p13^suc1 dimer, in which the individual p13^suc1 subunits had a globular conformation. This disparity was resolved when we found that the globular p13^suc1 fold undergoes a conformational transition into nonglobular monomers upon dissociation of the dimers following chelation of the zinc ions by ethylenediaminetetraacetic acid (EDTA). We also found that p13^suc1, but not p9^cksphy, forms stable dimers in the absence of metal ions. The topology of these EDTA-insensitive dimers likely resembles that of the human p9^ckshs2 protein, characterized by β4 strand exchange from each nonglobular monomer.