A. Hallmann, Enzymes in the extracellular matrix of Volvox: an inducible, calcium-dependent phosphatase with a modular composition, J BIOL CHEM, 274(3), 1999, pp. 1691-1697
The volvocine algae provide the unique opportunity for exploring developmen
t of an extracellular matrix. Volvox is the most advanced member of this fa
mily and represents the simplest multicellular organism, with differentiate
d cells, a complete division of labor, and a complex extracellular matrix,
which serves structural and enzymatic functions. In Volvox carteri a glycos
ylated extracellular phosphatase was identified, which is partially release
d from the extracellular matrix into the growth medium. The phosphatase is
synthesized in response to inorganic phosphate starvation and is strictly t
o inorganic phosphate starvation and is strictly calcium-dependent. The met
alloenzyme has been purified to homogeneity and characterized. Its gene and
cDNA have been cloned. Comparisons of genomic and cDNA sequences revealed
an extremely intron-rich gene (32 introns), With an apparent molecular mass
of 160 kDa the Volvox extracellular phosphatase is the largest phosphatase
cloned, with no sequence similarity to any other phosphatase. This enzyme
exhibits a modular composition. There are two large domains and a small one
. The large domains are highly homologous to each other and therefore most
likely originated from gene duplication and fusion. At least one EF-hand mo
tif for calcium binding was identified in this extracellular protein Volvox
extracellular phosphatase is the first calcium-dependent extracellular pho
sphatase to be cloned.