D. Applegate et al., CLONING AND EXPRESSION OF A NOVEL ACIDIC CALPONIN ISOFORM FROM RAT AORTIC VASCULAR SMOOTH-MUSCLE, The Journal of biological chemistry, 269(14), 1994, pp. 10683-10690
The actin-binding protein calponin has been implicated in the regulati
on of smooth muscle contraction. We have isolated cDNA clones encoding
a novel acidic calponin isoform from rat aortic vascular smooth muscl
e cells. The initial 273 residues of the deduced 330 amino acid polype
ptide (M(r) 36,377) are highly homologous to basic smooth muscle calpo
nin isoforms, but the remaining 57 residues at the carboxyl terminus c
omprise a unique and strongly acidic domain. The sequence of the acidi
c domain shows high homology (93.3% identity) to the partial sequence
of HUMXT01244, an unidentified human hippocampal gene product (Adams,
M., Dubnick, M., Kerlavgne, A. R., Moreno, R., Kelly, J. M., Utterback
, T. R., Nagle, J. W., Fields, C., and Venter, J. C. (1992) Nature 355
, 632-634). Transcripts encoding acidic calponin are expressed in cult
ured rat aortic vascular smooth muscle cells and in non-muscle and smo
oth muscle tissues of adult rat. Based on its calculated M(r) and the
tissue distribution of its expression, acidic calponin is an excellent
candidate for a previously detected non-muscle calponin homolog (Take
uchi, K., Takahashi, It., Abe, M., Nishida, W, Hiwada, K., Nabeya, T,
and Maruyama, It. (1991) J. Biochem. (Tokyo) 109, 311-316). Like basic
calponin isoforms, acidic calponin synthesized in a bacterial express
ion system bound F-actin. However, unlike basic calponin, the acidic i
soform did not interact with Ca2+/calmodulin, indicating a functional
distinction between the muscle and non-muscle forms.