title: Pcp4l1 contains an auto-inhibitory element that prevents its IQ motif from binding to calmodulin.
abstract: Purkinje cell protein 4-like 1 (Pcp4l1) is a small neuronal IQ motif protein closely related to the calmodulin-binding protein Pcp4/PEP-19. PEP-19 interacts with calmodulin via its IQ motif to inhibit calmodulin-dependent enzymes and we hypothesized Pcp4l1 would have similar properties. Surprisingly, full-length Pcp4l1 does not interact with calmodulin in yeast two-hybrid or pulldown experiments yet a synthetic peptide constituting only the IQ motif of Pcp4l1 binds calmodulin and inhibits calmodulin-dependent kinase II. A nine-residue glutamic acid-rich sequence in Pcp4l1 confers these unexpected properties. This element lies outside the IQ motif and its deletion or exchange with the homologous region of PEP-19 restores calmodulin binding. Conversion of a single isoleucine (Ile36) within this motif to phenylalanine, the residue present in PEP-19, imparts calmodulin binding onto Pcp4l1. Moreover, only aromatic amino acid substitutions at position 36 in Pcp4l1 allow binding. Thus, despite their sequence similarities PEP-19 and Pcp4l1 have distinct properties with the latter harboring an element that can functionally suppress an IQ motif. We speculate Pcp4l1 may be a latent calmodulin inhibitor regulated by post-translational modification and/or co-factor interactions.
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, Oxford, UK. jim.morgan@stjude.org
authors.forename: Marc A J
authors.initials: MA
authors.lastname: Morgan
authors.forename: James I
authors.initials: JI
authors.lastname: Morgan
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D002147:Calmodulin / Q000378:metabolism*; D002148:Calmodulin-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D014162:Transfection; D020798:Two-Hybrid System Techniques
chemical_list: D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D009419:Nerve Tissue Proteins; C493006:Pcp4l1 protein, mouse