SAS1B protein [ovastacin] shows temporal and spatial restriction to oocytes in several eutherian orders and initiates translation at the primary to secondary follicle transition

Abstract

Background Sperm Acrosomal SLLP1 Binding (SAS1B) protein (ovastacin) is an oolemmal binding partner for the intra-acrosomal sperm protein SLLP1. Results Immunohistochemical localization revealed that SAS1B translation is restricted among adult tissues to the ovary and oocytes, SAS1B appearing first in follicles at the primary-secondary transition. Quiescent oocytes within primordial follicles and primary follicles did not stain for SAS1B. Examination of neonatal rat ovaries revealed SAS1B expression first as faint signals in postnatal day 3 oocytes, with SAS1B protein staining intensifying with oocyte growth. Irrespective of animal age or estrus stage, SAS1B was seen only in oocytes of follicles that initiated a second granulosa cell layer. The precise temporal and spatial onset of SAS1B expression was conserved in adult ovaries in 7 eutherian species, including non-human primates. Immunoelectron micrographs localized SAS1B within cortical granules in MII oocytes. A population of SAS1B localized on the oolemma predominantly in the microvillar region anti-podal to the nucleus in ovulated MII rat oocytes and on the oolemma in macaque GV oocytes. Conclusions The restricted expression of SAS1B protein in growing oocytes, absence in the ovarian reserve, and localization on the oolemma suggest this zinc metalloprotease deserves consideration as a candidate target for reversible female contraceptive strategies.

Membrane associated cancer-oocyte neoantigen SAS1B/ovastacin is a candidate immunotherapeutic target for uterine tumors

“…SAS1B ( s perm a crosomal S LLP 1 b inding protein, a.k.a ovastacin, astacin-like or ASTL, GenBank ID NM_001002036.3), is a cortical granule and oocyte surface-associated zinc matrix metallo-proteinase (MMP, EC 3.4.24.21) with reported roles in sperm-egg interaction [ 1 , 2 ] and in the block to polyspermy [ 3 ] during eutherian fertilization. Beginning at its N-terminus this ∼46 kDa metalloproteinase consists of a signal peptide, pro-peptide motif, proteinase domain containing an active hex-box [HEXXHXXGXXH) catalytic site motif, and a unique C terminus [ 2 ].…”

“…SAS1B ( s perm a crosomal S LLP 1 b inding protein, a.k.a ovastacin, astacin-like or ASTL, GenBank ID NM_001002036.3), is a cortical granule and oocyte surface-associated zinc matrix metallo-proteinase (MMP, EC 3.4.24.21) with reported roles in sperm-egg interaction [ 1 , 2 ] and in the block to polyspermy [ 3 ] during eutherian fertilization. Beginning at its N-terminus this ∼46 kDa metalloproteinase consists of a signal peptide, pro-peptide motif, proteinase domain containing an active hex-box [HEXXHXXGXXH) catalytic site motif, and a unique C terminus [ 2 ]. The pattern of SAS1B protein expression within the ovary is conserved in several mammalian groups including non-human primates, canines, felines, artiodactyls, and rodents where SAS1B protein is restricted to the pool of growing oocytes beginning within primary-secondary transition follicles and persisting through ovulation [ 2 ].…”

Sperm Lysozyme-Like Protein 1 (SLLP1), an intra-acrosomal oolemmal-binding sperm protein, reveals filamentous organization in protein crystal form

“…An oolemma receptor for SLLP1, SAS1B, also known as ovastacin (Quesada et al ., ), is an astacin‐like metalloproteinase associated with the oocyte cortical granules (Burkart et al ., ; Pires et al ., ), oocyte membrane, and microvillar region (Sachdev et al ., ). Non‐glycosylated recombinant mSAS1B was reported to bind to mSLLP1 (Sachdev et al ., ), indicating the importance of protein–protein interaction irrespective of the presence of glycans.…”

“…Sperm Acrosomal SLLP1 Binding protein (ovastacin) has been reported to spatially localize to both the oolemma (Sachdev et al ., ) and cortical granules (Burkart et al ., ; Pires et al ., ) with different possible functions ascribed to the proteins in these locations. Before the cortical reaction, the enzymatic activity of SAS1B has been shown to be mediated by fetuin‐B (Dietzel et al ., ; Stocker et al ., ).…”

“…Knockout (Burkart et al ., ; Sachdev et al ., ) of the SLLP1 oolemmal‐binding partner protein SAS1B in mice resulted in sub‐fertility. In addition, SAS1B protein (ovastacin) has also been demonstrated to localize in cortical granules in the sub‐oolemmal cytoplasm (Pires et al ., ) with ZP2‐cleavage activity (Burkart et al ., ; Avella et al ., ) that could be inhibited by fetuin‐B (Dietzel et al ., ; Stocker et al ., ), which reflects its role in the block to polyspermy following fertilization. Moreover, our recent study shows the presence of six alternative splice variants for SAS1B (Sachdev et al ., ), which may relate to the versatile roles this protein plays during fertilization.…”