Plus and minus sexual agglutinins from Chlamydomonas reinhardtii.
Gametes of the unicellular green alga Chlamydomonas reinhardtii undergo sexual adhesion via enormous chimeric Hyp-rich glycoproteins (HRGPs), the plus and minus sexual agglutinins, that are displayed on their flagellar membrane surfaces. We have previously purified the agglutinins and analyzed their structural organization using electron microscopy. We report here the cloning and sequencing of the Sag1 and Sad1 genes that encode the two agglutinins and relate their derived amino acid sequences and predicted secondary structure to the morphology of the purified proteins. Both agglutinin proteins are organized into three distinct domains: a head, a shaft in a polyproline II configuration, and an N-terminal domain. The plus and minus heads are related in overall organization but poorly conserved in sequence except for two regions of predicted hydrophobic alpha-helix. The shafts contain numerous repeats of the PPSPX motif previously identified in Gp1, a cell wall HRGP. We propose that the head domains engage in autolectin associations with the distal termini of their own shafts and suggest ways that adhesion may involve head-head interactions, exolectin interactions between the heads and shafts of opposite type, and antiparallel shaft-shaft interactions mediated by carbohydrates displayed in polyproline II configurations.
Ferris
Patrick J
PJ
Department of Biology, Washington University, St. Louis, Missouri 63130, USA.
Waffenschmidt
Sabine
S
Umen
James G
JG
Lin
Huawen
H
Lee
Jae-Hyeok
JH
Ishida
Koichi
K
Kubo
Takeaki
T
Lau
Jeffrey
J
Goodenough
Ursula W
UW
D000373:Agglutinins / Q000235:genetics*; D000595:Amino Acid Sequence; D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000235:genetics*; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D015800:Protozoan Proteins / Q000235:genetics*; D011993:Recombinant Fusion Proteins / Q000235:genetics; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D000373:Agglutinins; D015800:Protozoan Proteins; D011993:Recombinant Fusion Proteins