Drosophila contains three genes that encode distinct isoforms of protein phosphatase 1

Abstract

The sequences of two Drosophilu and one rabbit protein phosphatase (PP) 1 catalytic subunits were determined from their cDNA. The sequence of Drosophilu PP1al was deduced from a 2.2-kb cDNA purified from an embryonic cDNA library, while that for Drosophilu PPlP was obtained from overlapping clones isolated from both a head cDNA library and an eye imaginal disc cDNA library. The gene for Drosophilu P P l q is at 96A2-5 on chromosome 3 and encodes a protein of 327 amino acids with a calculated molecular mass of 37.3 kDa. The gene for Drosophila PPlp is localized at 9C1-2 on the X chromosome and encodes a protein of 330 amino acids with a predicted molecular mass of 37.8 kDa. PPlal shows 96% amino acid sequence identity to PP1a2 (302 amino acids), an isoform whose gene is located in the 87B6-12 region of chromsome 3 [Dombradi, V., Axton and PPlg (327 amino acids), respectively, demonstrating that the structures of both isoforms are among the most conserved proteins known throughout the evolution of the animal kingdom. The presence of characteristic structural differences between PPla and PPl P, which have been preserved from insects to mammals, implies that the a and fi isoforms may have distinct biological functions.Protein phosphatase (PP) 1 is one of the four major types of protein serinelthreonine phosphatase that have been identified in eukaryotic cells [l]. Like PP2A and PP2C, PPl is able to dephosphorylate a number of phosphoproteins in vitro, raising the important question of which protein phosphatase dephosphorylates which substrates in vivo. As one approach to address this question, we have embarked on the cloning of each of these protein phosphatases in the fruit fly Drosophilu melunoguster as the first step towards obtaining mutants defective in each of these enzymes.Recently, we isolated a cDNA encoding a protein phosphatase whose predicted amino acid sequence showed 92% identity with that of PPla from rabbit skeletal muscle over the 302 homologous amino acids [2]. This cDNA hybridised strongly to the 87B6-12 region on chromosome 3, and more weakly to three other loci, namely 96A2-5 on chromosome 3, 9C1-2 on chromosome X and 13C1-2 on chromosome X. Note. Several years ago we isolated a cDNA from a rabbit skeletal muscle library encoding a protein identical to protein phosphatase (PP) l a in nucleotide and amino acid sequence, except at the extreme N-terminus of the coding region and in the 5' untranslated region. This cDNA was initially termed P P l j [8], but as discussed in [20] we now believe it is likely to have been a cloning artefact, since the same 5' region has subsequently been found fused to a quite different gene. Consequently it is no longer referred to as PPlD. These findings suggested that several genes encoding different isoforms of PP1 might be present in Drosophilu. In support of this contention, a cDNA was isolated that comprised part of the coding region of a further form of PP1 [2, 31. Here, we have completed the amino acid sequence of this isoform, which localises to 9C1-2, and d...

Disruption of the Striated Muscle Glycogen Targeting Subunit PPP1R3A of Protein Phosphatase 1 Leads to Increased Weight Gain, Fat Deposition, and Development of Insulin Resistance

“…In addition, our data show that G M specifically interacts with PP1␤ and not other isoforms of PP1 (Fig. 6B), consistent with previous studies (32,33). The increased weight gain of G M Ϫ/Ϫ mice from 3 months of age and massive increases in adipose tissue present at 12 months of age are consistent with the concept that when blood glucose cannot be converted into glycogen in skeletal muscle, much of this glucose is taken up by adipocytes and converted into fat deposits, which increase gradually with the age and lead to obesity.…”

The control of protein phosphatase‐1 by targetting subunits

“…Interestingly, the B isoform is also the major species of PPlC present in the targetted forms of PP1 in rabbit skclctal musclc, namcly PP1 G [44] and PPlM [18]. The finding that the sequences derived from the catalytic subunit of avian smooth-muscle PP1 M were identical to sequences found in mammalian PP1 fi, confirms the remarkable structural conservation of PPlC during evolution [41].…”

Defective insulin response of phosphorylase phosphatase in insulin-resistant humans.

“…Similar okadaic acid inhibition results for assays with either substrate suggest that distinct catalytic subunits would probably be isoforms of PP-1. Isoforms have been identified in tissues from rat (34) and Drosphila (35). Increasing glycogen can inhibit glycogen synthase phosphatase (15).…”