Enzymatic and Chemical Cleavage of the Core Light-Harvesting Polypeptides of Photosynthetic Bacteria: Determination of the Minimal Polypeptide Size and Structure Required for Subunit and Light-Harvesting Complex Formation

Kelley A. Meadows, Kouji Iida, Kazuichi Tsuda, Paul A. Recchia, Barbara A. Heller, Barbara Antonio, Mamoru Nango, Paul A Loach*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

67 Scopus citations

Abstract

To ascertain the minimal structural requirements for formation of the subunit and core lightharvesting complex (LH1), the α- and β-polypeptides of the LH1 from three purple photosynthetic bacteria were enzymatically or chemically truncated or modified. These polypeptides were then used in reconstitution experiments with bacteriochlorophyll a (BChla), and the formation of subunit and LH1 complexes was evaluated using absorbance and circular dichroism spectroscopies. Truncation or modification outside of the conserved core sequence region of the polypeptides had no effect on subunit or LH1 formation. However, the extent of formation and stability of the subunit and LH1 decreased as the polypeptide was shortened inside the core region within the N-terminal domain. This behavior was suggested to be due to the loss of potential ion-pairing and/or hydrogen-bonding interactions between the polypeptides. While the spectroscopic properties of the subunit complexes generated using truncated polypeptides were analogous to those obtained using native polypeptides, in some cases the resulting LH1 complex absorption was blue-shifted relative to the control. Thus, truncation within the N-terminal domain may have long-range effects on the immediate BChla binding environment, since the putative BChla binding site resides near the C-terminal end of the polypeptides. It was also demonstrated that the His located within the membrane-spanning domain on the N-terminal end of the β-polypeptide is not participating in ligation of the BChla in the reconstituted subunit and therefore probably not in LH1.

Original languageEnglish (US)
Pages (from-to)1559-1574
Number of pages16
JournalBiochemistry
Volume34
Issue number5
DOIs
StatePublished - Jan 1 1995

ASJC Scopus subject areas

  • Biochemistry

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