Determination of the B820 Subunit Size of a Bacterial Core Light-Harvesting Complex by Small-Angle Neutron Scattering

详细信息    查看全文

• 作者：Zheng-Yu Wang ; Yoshiyuki Muraoka ; Michihiro Nagao ; Mitsuhiro Shibayama ; Masayuki Kobayashi ; and Tsunenori Nozawa
• 刊名：Biochemistry
• 出版年：2003
• 出版时间：October 7, 2003
• 年：2003
• 卷：42
• 期：39
• 页码：11555 - 11560
• 全文大小：71K
• 年卷期：v.42,no.39(October 7, 2003)
• ISSN：1520-4995

文摘

The B820 subunit is an integral pigment-membrane protein complex and can be obtained byboth dissociation of the core light-harvesting complex (LH1) in photosynthetic bacteria and reconstitutionfrom its component parts in the presence of n-octyl -D-glucopyranoside (OG). Intrinsic size of the B820subunit from Rhodospirillum rubrum LH1 complex was measured by small-angle neutron scattering inperdeuterated OG solution and evaluated by Guinier analysis. Both the B820 subunits prepared bydissociation of LH1 and reconstitution from apopolypeptides and pigments were shown to have a molecularweight of 11 400 ± 500 and radius of gyration of 11.0 ± 1.0 Å, corresponding to a heterodimer consistingof one pair of -polypeptides and two bacteriochlorophyll a molecules. Molecular weights of micellesformed by OG alone in solutions were determined in a range from 30 000 to 50 000 over concentrationsof 1-5% (w/v), and thus are much larger than that of the B820 subunit. Similar measurement on thepigment-depleted apopolypeptides revealed highly heterogeneous behavior in the OG solutions, indicatingthat aggregates with various sizes were formed. The result provides evidence that bacteriochlorophyll amolecules play a crucial role in stabilizing and maintaining the B820 subunits in the dimeric state insolution. Further measurements on individual - and -polypeptides exhibited a marked difference inaggregation property between the two polypeptides. The -polypeptides appear to be uniformly dissolvedin OG solution in a monomeric form, whereas the -polypeptides favor a self-associated form and tendto form large aggregates even in the presence of detergent. The difference in aggregation tendency wasdiscussed in relation to the different behavior between - and -polypeptides in reconstitution withbacteriochlorophyll a molecules.