PROBING PROTEIN STRUCTURAL REQUIREMENTS FOR FORMATION OF THE CORE LIGHT-HARVESTING COMPLEX OF PHOTOSYNTHETIC BACTERIA USING HYBRID RECONSTITUTION METHODOLOGY
Pa. Loach et al., PROBING PROTEIN STRUCTURAL REQUIREMENTS FOR FORMATION OF THE CORE LIGHT-HARVESTING COMPLEX OF PHOTOSYNTHETIC BACTERIA USING HYBRID RECONSTITUTION METHODOLOGY, Photosynthesis research, 40(3), 1994, pp. 231-245
The alpha- and beta-polypeptides of LH1 isolated from four different p
hotosynthetic bacteria (Rhodospirillum rubrum, Rhodobacter sphaeroides
, Rhodobacter capsulatus and Rhodopseudomonas viridis) were used for h
omologous and hybrid reconstitution experiments with bacteriochlorophy
ll a. Formation of B820-type subunit complexes and LH1-type complexes
were evaluated. The beta-polypeptides of R. rubrum, Rb. sphaeroides an
d Rb. capsulatus behaved similarly and formed B820-type subunit comple
xes in the absence of an alpha-polypeptide. The alpha- and beta-polype
ptides were both required to form a LH1-type complex with each of thes
e three homologous systems. In hybrid experiments where the beta-polyp
eptides were tested for reconstitution with alpha-polypeptides other t
han their homologous partners, half of the twelve possible combination
s resulted in formation of both B820- and LH1-type complexes. Three of
the combinations that did not result in formation of a LH1-type compl
ex involved the beta-polypeptide of R. rubrum. It is suggested that th
ese latter results can be explained by charge repulsion between the Ly
s at position -17 (assigning the conserved His located nearest to the
C-terminus as position 0) in the beta-polypeptide of R. rubrum and eac
h of the heterologous alpha-polypeptides tested, all of which have an
Arg at this location. Conclusions that can be derived from these exper
imental results include: (1) the experimental data support the idea th
at a central core region of approximately 40 amino acids exists in eac
h of the polypeptides, which contains sufficient information to allow
formation of both the B820- and LH1-type complexes and (2) a specific
portion of the N-terminal hydrophilic region of each polypeptide was f
ound in which ion pairs between oppositely charged groups on the alpha
- and beta-polypeptides seem to stabilize complex formation.