Ra. Cardullo et al., SPERACT RECEPTORS ARE LOCALIZED ON SEA-URCHIN SPERM FLAGELLA USING A FLUORESCENT PEPTIDE ANALOG, Developmental biology, 162(2), 1994, pp. 600-607
In two species of sea urchins, Strongylocentrotus purpuratus and Lytec
hinus pictus, the egg jelly-associated decapeptide, speract, binds to
specific sperm surface receptors resulting in increased sperm motility
and respiration rate. Previously, a peptide analog, GGG[Y2]-speract,
was used to identify a 77-kDa receptor on intact sperm cells using che
mical cross-linking. In this paper we describe the synthesis and chara
cterization of a fluorescent derivative of GGG[Y2]-speract for use as
a probe for the sperm receptor. Fluorescein isothiocyanate (FITC) was
conjugated to the amino terminus of GGG[Y2]-speract and the resulting
analog (FITC-GGG[Y2]-speract) was purified by size exclusion chromatog
raphy and reverse-phase HPLC. Competition binding studies with the flu
orescent peptide and intact spermatozoa yielded IC50 values which were
indistinguishable from native speract and GGG[Y2]-speract (approximat
ely 20 nM). FITC-GGG[Y2]-speract half-maximally stimulated sperm respi
ration at a concentration nearly identical to that of the native pepti
de (EC50 approximately 50 pM). Using digitally enhanced video imaging
fluorescence microscopy, FITC-GGG[Y2]-speract was used to localize the
speract receptor on the flagella of intact sperm. Excess concentratio
ns of both unlabeled speract and GGG[Y2]-speract abolished the binding
of the fluorescent analog, yet unrelated peptides did not. Further, r
esults of cross-linking experiments using I-125-GGG[Y2]-speract and pu
rified sperm flagella and heads were consistent with the fluorescent l
abeling results on whole cells. The finding that the speract receptor
is localized exclusively to the sperm flagella may reveal its role in
the regulation of flagellar motility. (C) 1994 Academic Press, Inc.