A. Pereverzev et al., STRUCTURAL DIVERSITY OF THE VOLTAGE-DEPENDENT CA2-SUBUNIT( CHANNEL ALPHA(1E)), European journal of neuroscience, 10(3), 1998, pp. 916-925
Voltage-operated Ca2+ channels are heteromultimeric proteins. Their st
ructural diversity is caused by several genes encoding homologous subu
nits and by alternative splicing of single transcripts. Isoforms of al
subunits, which contain the ion conducting pore, have been deduced fr
om each of the six cDNA sequences cloned so far from different species
. The isoforms predicted for the alpha(1E) subunit are structurally re
lated to the primary sequence of the amino terminus, the centre of the
subunit (II-III loop), and the carboxy terminus. Mouse and human alph
a(1E) transcripts have been analysed by reverse transcription-polymera
se chain reaction and by sequencing of amplified fragments. For the II
-III loop three different alpha(1E) cDNA fragments are amplified from
mouse and human brain, showing that isoforms originally predicted from
sequence alignment of different species are expressed in a single one
. Both predicted alpha(1E) cDNA fragments of the carboxy terminus are
identified in vivo, Two different alpha(1E) constructs, referring to t
he major structural difference in the carboxy terminus, were stably tr
ansfected in HEK293 cells. The biophysical properties of these cells w
ere compared in order to evaluate the importance in vitro of the carbo
xy terminal insertion found in vivo. The wild-type alpha(1E) subunit s
howed properties, typical for a high-voltage activated Ca2+ channel. T
he deletion of 43 amino acid residues at the carboxy terminus does not
cause significant differences in the current density and the basic bi
ophysical properties. However, a functional difference is suggested, a
s in embryonic stem cells, differentiated in vitro to neuronal cells,
the pattern of transcripts indicative for different alpha(1E) isoforms
changes during development. In human cerebellum the longer alpha(1E)
isoform is expressed predominantly. Although, it has not been possible
to assign functional differences to the two alpha(1E) constructs test
ed in vitro, the expression pattern of the structurally related isofor
ms may have functional importance in vivo.