Poster: Organelle Biogenesis
Abs #
1152: Coordinated regulation and complex formation of FtsH metalloproteases in thylakoid membranes of chloroplasts
We have recently characterized leaf-variegated mutants yellow variegated (var1 and var2) in Arabidopsis. VAR1 and VAR2 are different loci but both encode a similar ATP-dependent metalloprotease homologous to bacterial FtsH and located in thylakoid membranes of chloroplasts. FtsH belongs to a subgroup of AAA+ protein super family and has been suggested to participate in various cellular functions. VAR1 and VAR2 has conserved motifs for ATPase, such as Walker A and B motifs, second region of homology, and a zinc-binding site. Because the mutant leaves show a dramatic decrease in PSII activity under exposure to high light, both proteases are suggested to play a role in photoprotection of PSII, likely promoting turnover of the reaction center protein D1. Despite the similarity between VAR1 and VAR2, a mutation at either one locus is not complemented by the function of the other, suggesting that there may be a communication mechanism. To study this at the protein level, we generated polyclonal antibodies that distinguish VAR1 and VAR2 proteins. Immunoblot analysis using these antibodies showed that VAR1 protein levels dramatically decreased invar2 mutants, and conversely that VAR2 protein levels decreased in var1 mutants. Fractionation of thylakoid membranes by sucrose density gradient and gel filtration indicated that VAR1 and VAR2 were detected in the same fraction that apparently corresponds to the multimeric form. Taken together, these results indicate that VAR1 and VAR2 form a complex and that loss of either one protein leads to a selective degradation of the other at the post-translational level.
