LHCAR1 OF THE RED ALGA PORPHYRIDIUM-CRUENTUM ENCODES A POLYPEPTIDE OFTHE LHCI COMPLEX WITH 7 POTENTIAL CHLOROPHYLL A-BINDING RESIDUES THATARE CONSERVED IN MOST LHCS
S. Tan et al., LHCAR1 OF THE RED ALGA PORPHYRIDIUM-CRUENTUM ENCODES A POLYPEPTIDE OFTHE LHCI COMPLEX WITH 7 POTENTIAL CHLOROPHYLL A-BINDING RESIDUES THATARE CONSERVED IN MOST LHCS, Plant molecular biology, 33(1), 1997, pp. 157-167
The accessory light-harvesting polypeptides associated with photosyste
m I (LHCI)! in Porphyridium cruentum bind chlorophyll a, zeaxanthin an
d p-carotene. A cDNA library of P. cruentum was screened with an antis
erum specific to the LHCI polypeptides, and an 0.9 kb fragment was ide
ntified as coding for an LHCI polypeptide. This cDNA; which we named L
hcaR1, has an open reading frame encoding 222 amino acid residues incl
uding a putative transit peptide of 28 amino acids. Hydropathy analysi
s suggests that there are three transmembrane helices in the mature po
lypeptide. Each of the amino acid residues that bind chlorophyll (six
residues) and serve in stabilizing the helices in higher-plant LHCs ar
e conserved in helices I and 3 of P. cruentum LhcaR1. The N-terminal f
lanking regions of these two helices also show high sequence conservat
ion with other LHCs. Helix 2 contains a seventh putative chlorophyll-b
inding site, but resembles helix 2 of higher-plant LHCs to a lesser de
gree. A sequence motif of 11 residues found near the N-terminus and in
each of the three helices suggests the possibility that the red algal
LhcaR1 derives from a gene duplication. Polypeptides of the expected
molecular weight in six other red algae (Achrochaetium, Bangia, Callit
hamnion Cyanidium, Polysiphonia, Spermothamnion) were recognized by th
e antiserum to P. cruentum LHCI, indicating a wide distribution of LHC
I in rhodophytes.