Protein Phosphatase 1, Regulatory Subunit 1C (PPP1R1C)

PPP1R1C belongs to a group of PP1 inhibitory subunits that are themselves regulated by phosphorylation. The deduced 116-amino acid protein has a calculated molecular mass of 13.1 kD. IPP5 shares 45% amino acid identity with IPP1 (PPP1R1A), with highest similarity in the N-terminal inhibitory domain. The inhibitory domain spans residues 8 through 60 and includes a KIQF motif required for PP1 binding and a critical thr40 phosphorylation site. Northern blot analysis detected variable expression of 1.1-, 1.9-, and 3.8-kb IPP5 transcripts in human tissues. Expression was highest in heart and skeletal muscle, moderate in liver and testis, and weak in placenta. No expression was detected in other tissues examined. Western blot analysis detected a similar distribution of IPP5 protein.