Ca. Colville et Rs. Molday, PRIMARY STRUCTURE AND EXPRESSION OF THE HUMAN BETA-SUBUNIT AND RELATED PROTEINS OF THE ROD PHOTORECEPTOR CGMP-GATED CHANNEL, The Journal of biological chemistry, 271(51), 1996, pp. 32968-32974
The full-length cDNA for the beta-subunit of the human rod photorecept
or cyclic nucleotide-gated channel has been shown to encode a 1251-ami
no acid (similar to 140 kDa) polypeptide which, like its bovine counte
rpart, has an unusual bipartite structure. The C-terminal part corresp
onds to the previously reported ''subunit 2'' of the human rod channel
and contains the structural features of other cyclic nucleotide-gated
channel subunits including six putative membrane spanning segments, a
cyclic nucleotide binding domain, a voltage sensor motif, and a pore
region. The N-terminal part contains the human homolog of the bovine g
lutamic acid-rich protein called GARP. Western blots indicate that bot
h the native and heterologously expressed human beta subunit migrate a
nomalously as a 220-kDa polypeptide by SDS-gel electrophoresis. Two ot
her GARP variants, full-length GARP (f-GARP) and truncated GARP (t-GAR
P), are also present in human, bovine, and rat rod outer segments and
migrate as 120-140- and 55-62-kDa polypeptides, respectively. The bovi
ne f-GARP and t-GARP cDNAs code for proteins containing 590 amino acid
s and 299 amino acids, respectively. The first 571 amino acids of f-GA
RP and the first 291 amino acids of t-GARP are identical to the corres
ponding N-terminal amino acid sequence of the bovine beta-subunit. The
two GARP variants, themselves, are not tightly associated with the ro
d channel. These results indicate that mammalian rod outer segments co
ntain three alternatively spliced variants of GARP, one of which const
itutes the N-terminal part of the rod channel beta-subunit.