Gm. Souza et al., IDENTIFICATION OF 2 NOVEL DICTYOSTELIUM-DISCOIDEUM CYSTEINE PROTEINASES THAT CARRY N-ACETYLGLUCOSAMINE-1-P MODIFICATION, The Journal of biological chemistry, 270(48), 1995, pp. 28938-28945
Dictyostelium discoideum makes multiple developmentally regulated lyso
somal cysteine proteinases. One of these, a lysosomal enzyme called pr
oteinase I, contains a cluster of GlcNAc-alpha-1-P-Ser residues. We ca
ll this phosphoglycosylation. To study its function, a cDNA library fr
om vegetative cells was screened, and two novel cysteine proteinase cl
ones were characterized (cprD and cprE). Each of them has highly conse
rved regions expected for cysteine proteinases, but unlike any other,
each has a serine-rich domain containing three distinct motifs, poly-S
, SGSQ, and SGSG, cprD and cprE cDNAs were overexpressed in Dictyostel
ium and the active enzymes identified, cprD codes for a protein of app
roximately 36 kDa (CP4), which is recognized by monoclonal antibodies
against GlcNAc-1-P and fucose, cprE corresponds to a 29-kDa protein, w
hich is recognized by antibodies against GlcNAc-1-P. mRNA for both enz
ymes is present in the vegetative phase and increases during growth on
bacteria but decreases throughout development. When the formation of
the fruiting body is complete the mRNA for both messages is detected a
gain but in very low levels. Having cloned cDNAs for proteins that car
ry GlcNAc-1-P should allow us to probe the function of the carbohydrat
e in these putative lysosomal enzymes.