beta-Scruin, a homologue of the actin crosslinking protein scruin, is localized to the acrosomal vesicle of Limulus sperm

J Cell Sci. 1995 Oct:108 ( Pt 10):3155-62. doi: 10.1242/jcs.108.10.3155.


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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acrosome / metabolism
  • Actins / chemistry
  • Actins / genetics
  • Actins / metabolism*
  • Amino Acid Sequence
  • Animals
  • DNA, Complementary / genetics
  • DNA, Complementary / isolation & purification
  • Horseshoe Crabs / metabolism*
  • Male
  • Molecular Sequence Data
  • Phylogeny
  • Rabbits
  • Sequence Alignment
  • Sequence Analysis
  • Spermatozoa / metabolism*


  • Actins
  • DNA, Complementary
  • scruin protein, Horseshoe Crab

Associated data

  • GENBANK/Z47541