Examining the structural basis for the lipid stimulation of protein phosphatase 5

Christopher Anthony Sinclair, Purdue University

Abstract

Protein phosphatase 5 and its yeast homologue, protein phosphatase T1, are serine/threonine protein phosphatases of approximately 60-kDa that share 42% sequence identity. Protein phosphates 5 and T1 contain a C-terminal catalytic region related to protein phosphatases 1, 2A and calcineurin. Unlike these phosphatases, however, protein phosphatase 5 and T1 also contain an extended N-terminal region consisting of three tetratricopeptide repeats. Tetratricopeptide repeats, found in a variety of unrelated proteins, are 34 amino acid consensus sequence motifs that are believed to be involved in protein-protein interactions. While the in vivo functions of protein phosphatase 5 and T1 are not known, evidence suggests that protein phosphatase 5 may be involved in a variety of cellular processes including the regulation of ion channels, steroid signaling and the cell cycle. In vitro studies suggest that protein phosphatase 5 may be regulated by unsaturated fatty acids like arachidonic acid or its metabolites. The major objective of this report was to increase our understanding of the mechanisms by which protein phosphatase 5, and potentially protein phosphatase T1, may be stimulated by lipids. This report suggests that the tetratricopeptide repeat domain and C terminus of protein phosphatase 5 act to suppress catalysis. However, upon lipid interaction with the TPR domain, both of these regions release their inhibition in a coordinated manner resulting in increased phosphatase activity. Modulation of protein phosphatase 5 activity by the tetratricopeptide repeat domain and C terminus suggests that these regions themselves may be targets for in vivo regulation. Investigation of protein phosphatase T1 suggests that this enzyme is regulated in a manner distinct from that of protein phosphatase 5. This conclusion is supported by the finding that lipids do not activate protein phosphatase T1 toward all substrates and that the tetratricopeptide repeat domain did not appear to inhibit protein phosphatase activity. Also the C terminus of protein phosphatase T1 was not required for lipid activation and it did not suppress phosphatase activity. It is striking that two such closely related phosphatases appear so different in their regulation, however, the significance of this difference in vivo is yet to be understood.

Degree

Ph.D.

Advisors

Rossie, Purdue University.

Subject Area

Biochemistry

COinS