title: Calpain cleavage of the B isoform of Ins(1,4,5)P3 3-kinase separates the catalytic domain from the membrane anchoring domain.
abstract: Inositol (1,4,5)-trisphosphate [Ins(1,4,5)P3] is one of the key intracellular second messengers in cells and mobilizes Ca2+ stores in the ER (endoplasmic reticulum). Ins(1,4,5)P3 has a short half-life within the cell, and is rapidly metabolized through one of two pathways, one of which involves further phosphorylation of the inositol ring: Ins(1,4,5)P3 3-kinase (IP3-3K) phosphorylates Ins(1,4,5)P3, resulting in the formation of inositol (1,3,4,5)-tetrakisphosphate [Ins(1,3,4,5)P4]. There are three known isoforms of IP3-3K, designated IP3-3KA, IP3-3KB and IP3-3KC. These have differing N-termini, but highly conserved C-termini harbouring the catalytic domain. The three IP3-3K isoforms have different subcellular locations and the B-kinase is uniquely present in both cytosolic and membrane-bound pools. As it is the N-terminus of the B-kinase that differs most from the A- and C-kinases, we have hypothesized that this portion of the protein may be responsible for membrane localization. Although there are no known membrane-targeting protein motifs within the sequence of IP3-3KB, it is found to be tightly associated with the ER membrane. Here, we show that specific regions of the N-terminus of IP3-3KB are necessary and sufficient for efficient membrane localization of the protein. We also report that, in the presence of Ca2+, the kinase domain of IP3-3KB is cleaved from the membrane-anchoring region by calpain.
authors.affiliation: Department of Biochemistry, University of Bristol, Bristol BS8 1TD, UK.
authors.forename: Krupa
authors.initials: K
authors.lastname: Pattni
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Millard
authors.forename: George
authors.initials: G
authors.lastname: Banting
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002154:Calpain / Q000378:metabolism*; D020134:Catalytic Domain / Q000235:genetics; D002462:Cell Membrane / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006801:Humans; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D007527:Isoenzymes; D008164:Luminescent Proteins; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D017853:Phosphotransferases (Alcohol Group Acceptor); C051038:Inositol 1,4,5-trisphosphate 3-kinase; D002154:Calpain