Interactions between a minimal protein serine/threonine phosphatase and its phosphopeptide substrate sequence

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Protein phosphatases (PP) are crucial enzymes regulating cellular processes.
• Coliphage lambda encodes a protein phosphatase (PPlambda) with unknown structural and functional relationships to cellular PPs.
• Understanding minimal phosphatase structures can elucidate evolutionary pathways and catalytic mechanisms.

Purpose of the Study:

• To biochemically and mutationally characterize PPlambda.
• To compare PPlambda to the catalytic cores of cellular serine/threonine protein phosphatases (PP1 and PP5).
• To determine the minimal substrate requirements for PPlambda activity.

Main Methods:

• Bacterial expression of truncated PP1 and PP5 phosphatases.
• Biochemical assays using various substrates (casein, p-nitrophenyl phosphate, peptides).
• Mutational analysis of key residues and terminal deletions in phosphatase cores.
• Characterization of PPlambda mutants.

Main Results:

• PPlambda is equivalent to the minimal catalytic core of serine/threonine protein phosphatases.
• Recombinant PP1 and PP5 catalytic cores exhibit potent activity and substrate versatility similar to PPlambda.
• These cores are resistant to common phosphatase inhibitors (okadaic acid, microcystin-LR) and trypsin.
• Specific mutations in the PP1 core had minimal impact, suggesting a closer identity to PPlambda.
• Minimal phosphopeptide substrates for PPlambda require flanking amino acid residues.

Conclusions:

• PPlambda represents a minimal, highly active catalytic core of serine/threonine protein phosphatases.
• Truncated cellular phosphatase cores mimic PPlambda's properties, supporting evolutionary links.
• Substrate structure significantly influences PPlambda's metal ion binding and catalytic activity.