I found certain points of X. Liu et al.'s Technical Comment Response’s argument to be elusive (Response to Comment on "A G protein-coupled receptor is a plasma membrane receptor for the plant hormone abscisic acid," published online 9 November 2007, sciencemag.org/cgi/content/full/5852/914d).
In one sentence, the authors state, "TMHMM has underpredicted transmembrane domains in many instances (3), and the only other reported GPCR in Arabidopsis, GCR1 (4), was predicted to be a three-transmembrane protein by SOSUI...", but omit the fact that GCR1, and not GCR2, is clearly predicted as a 7-TM protein by TMHMM.
The authors refer to the published studies on mammalian LanC homologues, arguing that GCR2 is biochemically distinct. But there is no side-by-side comparison. They point out that "LANCL1-GFP was exclusively localized to the cytosol and nucleus but was absent from the plasma membrane (9)", but miss the fact that the same paper shows a clear membrane association of LANCL2-GFP. Thus, the difference between GCR2 and LANCL1 alone, even if experimentally confirmed, does not suggest distinct function of GCR2.
Huaiyu Sun
Salk Institute for Biological Sciences, La Jolla, CA 92186-5800, USA.
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