@article{helton_kojetin_cavanagh_horne_2002, title={Alternative splicing of a beta(4) subunit proline-rich motif regulates voltage-dependent gating and toxin block of Ca(v)2.1 Ca2+ channels}, volume={22}, DOI={10.1523/jneurosci.22-21-09331.2002}, abstractNote={Ca2+ channel β subunits modify α1 subunit gating properties through direct interactions with intracellular linker domains. In a previous report (Helton and Horne, 2002), we showed that alternative splicing of the β4 subunit had α1 subunit subtype-specific effects on Ca2+ channel activation and fast inactivation. We extend these findings in the present report to include effects on slow inactivation and block by the peptide toxin ω-conotoxin (CTx)-MVIIC. N-terminal deletion and site-directed mutagenesis experiments revealed that the effects of alternative splicing on toxin block and all aspects of gating could be attributed to a proline-rich motif found within N-terminal β4b amino acids 10–20. Interestingly, this motif is conserved within the third postsynaptic density-95 (PSD-95)/Discs large/zona occludens-1 domain of the distantly related membrane-associated guanylate kinase homolog, PSD-95. Sequence identity of ∼30% made possible the building of β4a and β4bthree-dimensional structural models using PSD-95 as the target sequence. The models (1) reveal that alternative splicing of the β4 N terminus results in dramatic differences in surface charge distribution and (2) localize the proline-rich motif of β4b to an extended arm structure that flanks what would be the equivalent of a highly modified PSD-95 carboxylate binding loop. Northern blot analysis revealed a markedly different pattern of distribution for β4a versus β4bin the human CNS. Whereas β4a is distributed throughout evolutionarily older regions of the CNS, β4b is concentrated heavily in the forebrain. These results raise interesting questions about the functional role that alternative splicing of the β4 subunit has played in the evolution of complex neural networks.}, number={21}, journal={Journal of Neuroscience}, author={Helton, T. D. and Kojetin, D. J. and Cavanagh, J. and Horne, W. A.}, year={2002}, pages={9331–9339} }
 @article{helton_horne_2002, title={Alternative splicing of the beta(4) subunit has alpha(1) subunit subtype-specific effects on Ca2+ channel gating}, volume={22}, number={5}, journal={Journal of Neuroscience}, author={Helton, T. D. and Horne, W. A.}, year={2002}, pages={1573–1582} }
 @article{krovetz_helton_crews_horne_2000, title={C-terminal alternative splicing changes the gating properties of a human spinal cord calcium channel alpha 1A subunit}, volume={20}, DOI={10.1523/jneurosci.20-20-07564.2000}, abstractNote={The calcium channel α1Asubunit gene codes for proteins with diverse structure and function. This diversity may be important for fine tuning neurotransmitter release at central and peripheral synapses. The α1AC terminus, which serves a critical role in processing information from intracellular signaling molecules, is capable of undergoing extensive alternative splicing. The purpose of this study was to determine the extent to which C-terminal alternative splicing affects some of the fundamental biophysical properties of α1Asubunits. Specifically, the biophysical properties of two alternatively spliced α1Asubunits were compared. One variant was identical to an isoform identified previously in human brain, and the other was a novel isoform isolated from human spinal cord. The variants differed by two amino acids (NP) in the extracellular linker between transmembrane segments IVS3 and IVS4 and in two C-terminal regions encoded by exons 37 and 44. Expression inXenopusoocytes demonstrated that the two variants were similar with respect to current–voltage relationships and the voltage dependence of steady-state activation and inactivation. However, the rates of activation, inactivation, deactivation, and recovery from inactivation were all significantly slower for the spinal cord variant. A chimeric strategy demonstrated that the inclusion of the sequence encoded by exon 44 specifically affects the rate of inactivation. These findings demonstrate that C-terminal structural changes alone can influence the way in which α1Asubunits respond to a depolarizing stimulus and add to the developing picture of the C terminus as a critical domain in the regulation of Ca2+channel function.}, number={20}, journal={Journal of Neuroscience}, author={Krovetz, H. S. and Helton, T. D. and Crews, A. L. and Horne, W. A.}, year={2000}, pages={7564–7570} }