J. Biol. Chem., Vol. 260, Issue 5, 2681-2686, Mar, 1985
Isolation, purification, and amino acid composition of the tunicate hemocyte Thy-1 homolog
MH Mansour, R DeLange and EL Cooper
A serologic cross-reacting homolog to rodent Thy-1 glycoproteins has been
isolated from hemocyte cell surfaces of the advanced invertebrate group of
tunicates. The Thy-1.1 cross-reacting antigenic activity was followed
during purification by inhibiting the binding of MRC OX7 monoclonal
antibody to pure rat brain Thy-1 in a soluble phase radioimmunoassay. After
solubilization in deoxycholate, tunicate hemocyte Thy-1.1 antigenic
activity was purified by affinity chromatography using an MRC OX7
monoclonal antibody affinity column, followed by gel filtration. A 602-fold
enrichment in the Thy-1.1 antigenic activity, with a yield of 55.6%
compared to the starting crude membrane fraction, was obtained. The
antigenic activity was associated with a single glycoprotein of molecular
size of 3.1 nm and molecular weight estimated at 27,000 by sodium dodecyl
sulfate- polyacrylamide gel electrophoresis (15% gels). Amino acid
composition of the purified molecule was compared by the S delta Q index of
differences in composition to mammalian and non-mammalian Thy-1
glycoproteins, Ig, major histocompatibility complex-encoded polypeptides,
beta 2-microglobulin, and other recognition molecules. With this parameter,
the tunicate hemocyte Thy-1 homology revealed significant relatedness to
avian and mammalian Thy-1 molecules and was interestingly more related to
mu chains of primitive vertebrates and to HLA class I and II encoded
polypeptides than to Thy-1 molecules of higher vertebrates. Based upon
these observations, the tunicate hemocyte Thy-1 homolog seems to represent
an ancestral Thy-1 molecule which, in structural terms, may represent an
invertebrate member of the Ig superfamily.
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