beta-Scruin, a homologue of the actin crosslinking protein scruin, is localized to the acrosomal vesicle of Limulus sperm.
Scruin (alpha-scruin) is an actin bundling protein found in the acrosomal process of Limulus polyhemus sperm. We have cloned and sequenced a second scruin isoform from Limulus, beta-scruin, that is 67% identical to alpha-scruin. Northern and Southern analyses confirm that beta-scruin and alpha-scruin are encoded by distinct genes. The sequence of beta-scruin, like alpha-scruin, is organized into N- and C-terminal superbarrel domains that are characterized by a six-fold repeat of a 50 residue motif. Western analysis using rabbit polyclonal antisera specific for alpha- and beta-scruin indicate that beta-scruin, like alpha-scruin, is found in Limulus sperm but not blood or muscle. Both immunofluorescence microscopy and immunogold-EM localize beta-scruin within the acrosomal vesicle at the anterior of sperm but not in the acrosomal process. The function of beta-scruin in this membrane-bounded compartment that is devoid of actin is unknown. However, the location of beta-scruin together with the fact that it contains two putative beta-superbarrel structural folds, which are known to be catalytic domains in a number of proteins, suggests it may have a possible enzymatic role.
Way
M
M
Whitehead Institute, Nine Cambridge Center, MA 02142, USA.
Sanders
M
M
Chafel
M
M
Tu
Y H
YH
Knight
A
A
Matsudaira
P
P
D000177:Acrosome / Q000378:metabolism; D000199:Actins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D018076:DNA, Complementary / Q000235:genetics / Q000302:isolation & purification; D006737:Horseshoe Crabs / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D010802:Phylogeny; D011817:Rabbits; D016415:Sequence Alignment; D017421:Sequence Analysis; D013094:Spermatozoa / Q000378:metabolism*
D000199:Actins; D018076:DNA, Complementary; C083765:scruin protein, Horseshoe Crab