A protein kinase screen of Neurospora crassa mutant strains reveals that the SNF1 protein kinase promotes glycogen synthase phosphorylation

Glycogen functions as a carbohydrate reserve in a variety of organisms and its metabolism is highly regulated. The activities of glycogen synthase and glycogen phosphorylase, the rate-limiting enzymes of the synthesis and degradation processes, respectively, are regulated by allosteric modulation and by reversible phosphorylation. To identify the protein kinases affecting glycogen metabolism in N. crassa, we performed a screen of 84 serine/threonine kinase knockout strains. We identified multiple kinases that have already been described as controlling glycogen metabolism in different organisms, such as NcSNF1, NcPHO85, NcGSK3, NcPKA, PSK2 homologue, and NcATG1. In addition, many hypothetical kinases have been implicated in the control of glycogen metabolism. Two kinases, NcIME-2 and NcNIMA already functionally characterized but with no functions related to glycogen metabolism regulation, were also identified. Among the kinases identified, it is important to mention the role of NcSNF1. We showed here that this kinase was implicated in glycogen synthase phosphorylation, as demonstrated by the higher levels of glycogen accumulated during growth, along with a higher glycogen synthase -/+ G6P activity ratio and a lesser set of phosphorylated GSN isoforms in strain Ncsnf1KO, when compared to the wild-type strain. The results led us to conclude that, in N. crassa, this kinase promotes phosphorylation of glycogen synthase either directly or indirectly, which is the opposite of...
Source: BJ Cell - Category: Biochemistry Authors: Tags: BJ Biomolecules Source Type: research