The evolutionarily conserved small actin-monomer binding protein profilin is believed to be a housekeeping factor that maintains a general pool of unassembled actin. However, despite similar primary sequences, structural folds, and affinities for G-actin and poly-L-proline, budding yeast profilin ScPFY fails to complement fission yeast profilin SpPRF temperature-sensitive mutant cdc3-124 cells. To identify profilin's essential properties, we built a combinatorial library of ScPFY variants containing either WT or SpPRF residues at multiple positions and carried out a genetic selection to isolate variants that support life in fission yeast. We subsequently engineered ScPFY(9-Mut), a variant containing nine substitutions in the actin-binding region, which complements cdc3-124 cells. ScPFY(9-Mut), but not WT ScPFY, suppresses severe cytokinesis defects in cdc3-124 cells. Furthermore, the major activity rescued by ScPFY(9-Mut) is the ability to enhance cytokinesis formin Cdc12-mediated actin assembly in vitro, which allows cells to assemble functional contractile rings. Therefore an essential role of profilin is to specifically facilitate formin-mediated actin assembly for cytokinesis in fission yeast.

• PMID: 25392301
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Journal Article | Research Support, N.I.H., Extramural | Research Support, Non-U.S. Gov't | Research Support, U.S. Gov't, Non-P.H.S.

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Bestul AJ, Christensen JR, Grzegorzewska AP, Burke TA, Sees JA, Carroll RT, Sirotkin V, Keenan RJ, Kovar DR

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