|
The egg coat, an extracellular matrix made up of glycoprotein filaments, plays a
key role in animal fertilization by acting as a gatekeeper for sperm. Egg coat
components polymerize using a common zona pellucida (ZP) "domain"
module that consists of two related immunoglobulin-like domains, called ZP-N and
ZP-C. The ZP module has also been recognized in a large number of other secreted
proteins with different biological functions, whose mutations are linked to
severe human diseases. During the last decade, tremendous progress has been made
toward understanding the atomic architecture of the ZP module and the structural
basis of its polymerization. Moreover, sperm-binding regions at the N-terminus
of mollusk and mammalian egg coat subunits were found to consist of domain
repeats that also adopt a ZP-N fold. This discovery revealed an unexpected link
between invertebrate and vertebrate fertilization and led to the first structure
of an egg coat-sperm protein recognition complex. In this review we summarize
these exciting findings, discuss their functional implications, and outline
future challenges that must be addressed in order to develop a comprehensive
view of this family of biomedically important extracellular molecules.
|
