PubMed Journals: J Biol Chem

  Source:		PMID: 3759968

    		J Biol Chem. 1986 Oct 5;261(28):13333-41.
			Sequence analysis of phospholamban. Identification
			of phosphorylation sites and two major structural

			Simmerman HK, Collins JH, Theibert JL, Wegener
			AD, Jones LR.

			Phospholamban is a regulatory protein in
			cardiac sarcoplasmic reticulum that is
			phosphorylated by cAMP- and
			Ca2+/calmodulin-dependent protein kinase
			activities. In this report, we present the
			partial amino acid sequence of canine cardiac
			phospholamban and the identification of
			the sites phosphorylated by these two protein
			kinases. Gas-phase protein sequencing was
			used to identify 20 NH2-terminal residues.
			Overlap peptides produced by trypsin or
			papain digestion extended the sequence 16
			residues to give the following primary structure:
			Leu-Leu-Leu-Ile-. Phospholamban phosphorylated
			by either cAMP-dependent or
			Ca2+/calmodulin-dependent protein kinase
			was cleaved with trypsin, and the major
			phosphorylated peptide (comprising greater
			than 70% of the incorporated 32P label)
			was purified by reverse-phase high performance
			liquid chromatography. The identical sequence
			was revealed for the radioactive peptide
			obtained from phospholamban phosphorylated
			by either kinase:
			The adjacent residues Ser7 and Thr8 of phospholamban
			were identified as the unique sites phosphorylated
			by cAMP- and Ca2+/calmodulin-dependent protein
			kinases, respectively. These results establish
			that phospholamban is an oligomer of small,
			identical polypeptide chains. A hydrophilic,
			cytoplasmically oriented NH2-terminal domain
			on each monomer contains the unique, adjacent
			residues phosphorylated by cAMP- and
			Ca2+/calmodulin-dependent protein kinase
			activities. Analysis by hydropathic profiling
			and secondary structure prediction suggests
			that phospholamban monomers also contain
			a hydrophobic domain, which could form amphipathic
			helices sufficiently long to traverse the
			sarcoplasmic reticulum membrane. A model
			of phospholamban as a pentamer is presented
			in which the amphipathic alpha-helix of
			each monomer is a subunit of the pentameric
			membrane-anchored domain, which is comprised
			of an exterior hydrophobic surface and an
			interior hydrophilic region containing polar
			side chains.

			PMID: 3759968 [Indexed for MEDLINE]

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