OVIDUCTINS POSSESS CHITINASE-LIKE AND MUCIN-LIKE DOMAINS - A LEAD IN THE SEARCH FOR THE BIOLOGICAL FUNCTION OF THESE OVIDUCT-SPECIFIC ZP-ASSOCIATING GLYCOPROTEINS

Over the last 10 years considerable progress has been made in the immu nological and biochemical characterization of oviduct-specific glycopr oteins. It is now well established that a subclass of these secretory products, designated as oviductins, associate with the zona pellucida of the ovulated oocyte and with the early embryo. Recent reports on th e cloning of cDNAs of oviductins from various species, including that of golden hamster (Mesocricetus auratus) oviductin by our laboratory, allowed us to compare their deduced amino acid sequences with those of other proteins. Optimal alignment analysis showed that oviductins con tain regions of significant similarity with catalytically inactive mam malian members of the bacterial and microfilarial chitinase protein fa mily. Most importantly, a close examination of the hamster and human d educed amino acid sequences revealed that both glycoproteins possess c ontiguous Ser/Thr rich repeated units, clustered in their carboxy-term inal portions. These mucin-type motifs are similar in the hamster and human glycoprotein, although hamster oviductin contains more of these complete units. This striking feature might indicate that these molecu les play a similar role to mucin-type glycoproteins, e.g., in protecti ng the oocyte and early embryo against attacks from their environment. We propose a model whereby oviductins are targeted to the oocyte via the interaction of their chitinase-like domains with specific oligosac charide moieties of the zona pellucida. Once localized to this structu re, oviductin molecules would act as a protective shield around the oo cyte and early embryo by Virtue of their densely glycosylated mucin-ty pe domains. (C) 1995 Wiley-Liss, Inc.