Alternative splicing of the voltage-gated Ca2+ channel beta4 subunit creates a uniquely folded N-terminal protein binding domain with cell-specific expression in the cerebellar cortex.
Ca2+ channel beta subunits regulate cell-surface expression and gating of voltage-dependent Ca2+ channel alpha1 subunits. Based on primary sequence comparisons, beta subunits are predicted to be modular structures composed of five domains (A-E) that are related to the large family of membrane-associated guanylate kinase proteins. The crystal structure of the beta subunit core B-D domains has been reported recently; however, little is known about the structures of the A and E domains. The N-terminal A domain differs among the four subtypes of Ca2+ channel beta subunits (beta1-beta4) primarily as the result of two duplications of an ancestral gene containing multiple alternatively spliced exons. At least nine A domain sequences can be generated by alternative splicing. In this report, we focus on one A domain sequence, the highly conserved beta4a A domain. We solved its three-dimensional structure and show that it is expressed in punctate structures throughout the molecular layer of the cerebellar cortex. We also demonstrate that it does not participate directly in Cav2.1 Ca2+ channel gating but serves as a binding site in protein-protein interactions with synaptotagmin I and the LC2 domain of microtubule-associated protein 1A. With respect to beta4 subunits, the interactions are specific for the beta4a splice variant, because they do not occur with the beta4b A domain. These results have strong bearing on our current understanding of the structure of alternatively spliced Ca2+ channel beta subunits and the cell-specific roles they play in the CNS.
Vendel
Andrew C
AC
Department of Biomedical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, Colorado 80526, USA.
Terry
Mark D
MD
Striegel
Amelia R
AR
Iverson
Nicole M
NM
Leuranguer
Valerie
V
Rithner
Christopher D
CD
Lyons
Barbara A
BA
Pickard
Gary E
GE
Tobet
Stuart A
SA
Horne
William A
WA
D017398:Alternative Splicing; D000818:Animals; D015153:Blotting, Western / Q000379:methods; D015220:Calcium Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism*; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D015870:Gene Expression / Q000502:physiology*; D015723:Gene Library; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D015640:Ion Channel Gating / Q000502:physiology; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects; D051379:Mice; D008810:Mice, Inbred C57BL; D008845:Microinjections / Q000379:methods; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009865:Oocytes; D018408:Patch-Clamp Techniques / Q000379:methods; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D050863:Synaptotagmin I / Q000378:metabolism; D020798:Two-Hybrid System Techniques; D014981:Xenopus
D015220:Calcium Channels; D011994:Recombinant Proteins; D050863:Synaptotagmin I