Topological switching of the COOH-terminal domain of peptidylglycine alpha-amidating monooxygenase by alternative RNA splicing.
Proteins encompassing the two catalytic domains (monooxygenase and lyase) and the COOH-terminal domain of rat peptidylglycine alpha-amidating monooxygenase (rPAM)3 were purified from recombinant Escherichia coli overexpressing each domain and used to raise domain-specific polyclonal antibodies. Four alternatively spliced forms of PAM RNA (PAM-1, -2, -3, and -4) were transcribed in vitro and used to synthesize PAM proteins in a cell-free translation system. The orientation of the proteins in microsomal membrane vesicles was analyzed using trypsin protection assays and immunoprecipitation with the domain-specific antibodies. Only one of the two potential N-glycosylation sites (Asn765-Phe-Ser) in PAM-1 was efficiently utilized by microsomal membranes. PAM-1 and PAM-2 were shown to be type Ia membrane proteins with their two catalytic domains residing within microsomal vesicles and their COOH-terminal domains exposed to the cytosol. In contrast, PAM-3 and PAM-4 were shown to be soluble proteins contained entirely within vesicles. Thus, the COOH-terminal domain underwent topological switching between the cytosolic (PAM-1 and -2) and luminal (PAM-3) compartments as a function of alternative splicing of exons Ba/Bb. Computer analyses of the PAM protein sequence correlated the exons encoding PAM-1 with a model for the structural and functional domains of the PAM protein. The dual topologies of the PAM proteins confer an important means of functional regulation to this secretory granule associated neuropeptide processing enzyme.
Yun
H Y
HY
Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Johnson
R C
RC
Mains
R E
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Eipper
B A
BA
D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000276:immunology; D001483:Base Sequence; D015153:Blotting, Western; D004285:Dogs; D000939:Epitopes / Q000276:immunology; D004926:Escherichia coli / Q000235:genetics; D005091:Exons; D015870:Gene Expression; D006031:Glycosylation; D007163:Immunosorbent Techniques; D007425:Intracellular Membranes / Q000201:enzymology; D008861:Microsomes / Q000201:enzymology / Q000648:ultrastructure; D006899:Mixed Function Oxygenases / Q000235:genetics* / Q000276:immunology / Q000302:isolation & purification; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes; D010446:Peptide Fragments / Q000276:immunology / Q000302:isolation & purification; D014176:Protein Biosynthesis; D012326:RNA Splicing; D012333:RNA, Messenger / Q000235:genetics; D011817:Rabbits; D051381:Rats; D011994:Recombinant Proteins / Q000276:immunology / Q000302:isolation & purification; D014357:Trypsin / Q000378:metabolism
D000906:Antibodies; D000939:Epitopes; D009097:Multienzyme Complexes; D010446:Peptide Fragments; D012333:RNA, Messenger; D011994:Recombinant Proteins; D006899:Mixed Function Oxygenases; C035189:peptidylglycine monooxygenase; D014357:Trypsin