Volume 272, Number 13,
Issue of March 28, 1997
pp. 8759-8763
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.
Novel Characteristics of a Myosin Isolated from Mammalian Retinal
Pigment Epithelial and Endothelial Cells
(Received for publication, August 22, 1996, and in revised form, November 22, 1996)
Mark C.
Alliegro
and
Laura A.
Linz
From the Department of Anatomy, Louisiana State University Medical
Center, New Orleans, Louisiana 70112
We have isolated a novel, high
Mr protein from human retinal pigment
epithelial cells and endothelial cells by affinity chromatography on
Sepharose 4B. Two polypeptides are present on SDS-gels of the 8 M urea eluent with apparent molecular mass of ~210 and 47 kDa. In the absence of dithiothreitol, the two polypeptides migrate as
one protein band with an apparent molecular mass of ~550 kDa. "Piglet," as this molecule is tentatively named, is present in retinal pigment epithelial and endothelial cells of several species, but could not be detected in the nonepithelial cells we examined. Immunofluorescent localization using an antibody to the 210-kDa polypeptide revealed a filamentous network in the cytoplasm of cultured
cells. This antibody was used to identify a cDNA for piglet in a
bovine aortic endothelial cell expression library. Sequence data
indicate a high degree of identity with non-muscle myosin II heavy
chain. We subsequently found that piglet had an actin-activated ATPase
activity, colocalized with actin in cells, and reacted on Western blots
with a pan-non-muscle myosin II heavy chain antiserum. The protein was
also recognized by antibodies specific for myosin heavy chain isoform
A, but did not react with anti-isoform B antibodies. Although piglet
has several features in common with known forms of non-muscle myosin
II, the distinctly unconventional features it displays suggest that it
is a novel myosin.