Journal of Neuroscience, Vol 9, 3631-3637, Copyright © 1989 by Society for Neuroscience
ARPP-21, a cyclic AMP-regulated phosphoprotein enriched in dopamine- innervated brain regions. I. Amino acid sequence of ARPP-21B from bovine caudate nucleus
KR Williams, HC Hemmings Jr, MB LoPresti and P Greengard
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06510.
ARPP-21 (cAMP-regulated phosphoprotein, Mr = 21,000 as determined by
SDS-PAGE) is a major cytosolic substrate for cAMP-stimulated protein
phosphorylation in dopamine-innervated regions of the rat CNS. It has
recently been purified to homogeneity from bovine caudate nucleus and
characterized (Hemmings and Greengard, 1989). ARPP-21 is isolated as 2
isoforms, ARPP-21A and ARPP-21B. The amino acid sequence of purified bovine
ARPP-21B has now been determined by gas-phase sequencing. The S-
14C-carboxymethylated protein was subjected to enzymatic cleavage with
trypsin, chymotrypsin, subtilisin, and endoproteinase Lys-C. The resulting
peptides were purified by high-performance liquid chromatography, and
selected peptides were subjected to amino acid analysis and/or amino acid
sequencing by automated Edman degradation. ARPP-21B consists of a single
NH2-terminal blocked polypeptide chain of 88 residues, with a calculated
molecular mass of 9561 Da, including an NH2-terminal acetyl group inferred
by deblocking with an acylaminopeptidase. This molecular mass is
significantly lower than earlier estimates based on SDS-PAGE or
hydrodynamic measurements. The seryl residue phosphorylated by
cAMP-dependent protein kinase (Hemmings et al., 1989) is located at
position 55. The molecule contains 1 cysteinyl residue, at position 71, and
contains no methionyl, tyrosyl, phenylalanyl, tryptophanyl, or histidinyl
residues. Determination of the primary structure of ARPP-21, one of several
phosphoproteins localized to dopaminoceptive neurons in the basal ganglia,
provides a framework for further investigations into the molecular
mechanisms involved in dopaminergic neurotransmission.