PARENT SESSION
Posters P4Aa Chlorophyll and bilin based antenna systems. Abstracts (239-271)

Investigation of PSI-associated light-harvesting proteins in a chromophyte alga. Fiona Bentley^*,1, Julia Harnett¹, Kenichiro Ishida², Beverley Green¹, ¹ Botany Department, Vancouver, BC, Canada² Department of Biology, Kanazawa, Japan

ABSTRACT- Green algae and higher plants use membrane-intrinsic antenna proteins that bind chlorophylls a and b, while brown and yellow algae (chromophytes) use similar proteins, the fucoxanthin chlorophyll a/c proteins (FCPs). They are all part of a very large protein family called the light-harvesting complex (LHC) family. Within the green algae/higher plant line these proteins diverged into LHCI- and LHCII-types based on their association with photosystem I (PSI) and photosystem II (PSII) respectively, but no such specialization has been found in algae with Chl a/c antennas. However, these algae obtained their plastids by secondary endosymbiosis from red algae, which have LHC proteins associated only with PSI and binding only Chl a. This raised an interesting question. Do chromophytes have specific PSI-associated LHC proteins? Two FCP gene sequences from Heterosigma that are more similar to PSI-associated red algal LHCs than to other FCP sequences from chromophyte algae support the possibility. Here we examined the antenna proteins of Heterosigma akashiwo, which has at least eight immunologically distinct FCPs of 16-21.5 kDa, to see if any were preferentially associated with PSI. PSI particles were purified by dodecyl maltoside (DM) solubilization and sucrose gradient fractionation. Proteins were then separated on a 12-16% polyacrylamide gel and immunoblotted with an FCP antibody. At least three polypeptides of 17.5, 18.5 and 19.5 kDa were found to be associated with PSI and a proteomics approach was used to identify and characterize these proteins. We thank the Natural Sciences and Engineering Council of Canada for financial support.

KEY WORDS: Heterosigma akashiwo, light-harvesting antenna, photosystem I, fucoxanthin chlorophyll a/c proteins