Five members of a novel Ca(2+)-binding protein (CABP) subfamily with similarity to calmodulin.
Five members of a novel Ca(2+)-binding protein subfamily (CaBP), with 46-58% sequence similarity to calmodulin (CaM), were identified in the vertebrate retina. Important differences between these Ca(2+)-binding proteins and CaM include alterations within their second EF-hand loop that render these motifs inactive in Ca(2+) coordination and the fact that their central alpha-helixes are extended by one alpha-helical turn. CaBP1 and CaBP2 contain a consensus sequence for N-terminal myristoylation, similar to members of the recoverin subfamily and are fatty acid acylated in vitro. The patterns of expression differ for each of the various members. Expression of CaBP5, for example, is restricted to retinal rod and cone bipolar cells. In contrast, CaBP1 has a more widespread pattern of expression. In the brain, CaBP1 is found in the cerebral cortex and hippocampus, and in the retina this protein is found in cone bipolar and amacrine cells. CaBP1 and CaBP2 are expressed as multiple, alternatively spliced variants, and in heterologous expression systems these forms show different patterns of subcellular localization. In reconstitution assays, CaBPs are able to substitute functionally for CaM. These data suggest that these novel CaBPs are an important component of Ca(2+)-mediated cellular signal transduction in the central nervous system where they may augment or substitute for CaM.
Haeseleer
F
F
Department of Ophthalmology, University of Washington, Seattle, Washington 98195, USA.
Sokal
I
I
Verlinde
C L
CL
Erdjument-Bromage
H
H
Tempst
P
P
Pronin
A N
AN
Benovic
J L
JL
Fariss
R N
RN
Palczewski
K
K
D000595:Amino Acid Sequence; D000818:Animals; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000235:genetics*; D002147:Calmodulin / Q000737:chemistry*; D002417:Cattle; D003001:Cloning, Molecular; D016384:Consensus Sequence; D020224:Expressed Sequence Tags; D015723:Gene Library; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009928:Organ Specificity; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry; D015183:Restriction Mapping; D012160:Retina / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D002135:Calcium-Binding Proteins; D002147:Calmodulin; D020033:Protein Isoforms; D011994:Recombinant Proteins