The PLAC1-homology region of the ZP domain is sufficient for protein polymerisation.
BACKGROUND
Hundreds of extracellular proteins polymerise into filaments and matrices by using zona pellucida (ZP) domains. ZP domain proteins perform highly diverse functions, ranging from structural to receptorial, and mutations in their genes are responsible for a number of severe human diseases. Recently, PLAC1, Oosp1-3, Papillote and CG16798 proteins were identified that share sequence homology with the N-terminal half of the ZP domain (ZP-N), but not with its C-terminal half (ZP-C). The functional significance of this partial conservation is unknown.


RESULTS
By exploiting a highly engineered bacterial strain, we expressed in soluble form the PLAC1-homology region of mammalian sperm receptor ZP3 as a fusion to maltose binding protein. Mass spectrometry showed that the 4 conserved Cys residues within the ZP-N moiety of the fusion protein adopt the same disulfide bond connectivity as in full-length native ZP3, indicating that it is correctly folded, and electron microscopy and biochemical analyses revealed that it assembles into filaments.


CONCLUSIONS
These findings provide a function for PLAC1-like proteins and, by showing that ZP-N is a biologically active folding unit, prompt a re-evaluation of the architecture of the ZP domain and its polymers. Furthermore, they suggest that ZP-C might play a regulatory role in the assembly of ZP domain protein complexes.
Jovine
Luca
L
Brookdale Department of Molecular, Cell and Developmental Biology, Mount Sinai School of Medicine, One Gustave L, Levy Place, New York, NY 10029-6574, USA. luca.jovine@biosci.ki.se
Janssen
William G
WG
Litscher
Eveline S
ES
Wassarman
Paul M
PM
D000818:Animals; D003001:Cloning, Molecular; D019281:Dimerization; D004527:Egg Proteins / Q000737:chemistry*; D008562:Membrane Glycoproteins / Q000737:chemistry*; D011108:Polymers; D011257:Pregnancy Proteins / Q000737:chemistry*; D011956:Receptors, Cell Surface / Q000737:chemistry*; D011994:Recombinant Proteins; D015044:Zona Pellucida / Q000737:chemistry*; D000072216:Zona Pellucida Glycoproteins
D004527:Egg Proteins; D008562:Membrane Glycoproteins; C415583:PLAC1 protein, human; D011108:Polymers; D011257:Pregnancy Proteins; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; C000606517:ZP3 protein, human; D000072216:Zona Pellucida Glycoproteins