Devrekanli A, Foltman M, Roncero C, Sanchez-Diaz A, Labib K

The chitin synthase that makes the primary septum during cell division in budding yeasts is an important therapeutic target with an unknown activation mechanism. We previously found that the C2-domain of the Saccharomyces cerevisiae Inn1 protein plays an essential but uncharacterised role at the cleavage site during cytokinesis. By combining ...

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a novel degron allele of INN1 with a point mutation in the C2-domain, we screened for mutations in other genes that suppress the resulting defect in cell division. In this way we identified 22 dominant mutations of CHS2 (Chitin Synthase II) that map to two neighbouring sites in the catalytic domain. Whereas Chs2 in isolated cell membranes is normally almost inactive, unless protease treatment is used to bypass inhibition, the dominant suppressor allele Chs2-V377I has enhanced activity in vitro. We show that Inn1 associates with Chs2 in yeast cell extracts, and interacts in the yeast two-hybrid assay with the amino-terminal 65% of Chs2 that contains the catalytic domain. In addition to compensating for mutations in the Inn1 C2-domain, the dominant CHS2 alleles also suppress cytokinesis defects produced by lack of the Cyk3 protein, and our data support a model whereby the C2-domain of Inn1 acts in conjunction with Cyk3 to regulate the catalytic domain of Chs2 during cytokinesis. These findings suggest novel approaches for developing future drugs against important fungal pathogens.

Date: Sep. 06, 2012

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