Three semidominant barley mutants with single amino acid substitutions in the smallest magnesium chelatase subunit form defective AAA+ hexamers

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Three semidominant barley mutants with single amino acid substitutions in the smallest magnesium chelatase subunit form defective AAA+ hexamers. / Hansson, Andreas; Willows, R D; Roberts, T H; Hansson, Mats.

I: Proceedings of the National Academy of Sciences, Vol. 99, Nr. 21, 2002, s. 13944-13949.

Forskningsoutput: TidskriftsbidragArtikel i vetenskaplig tidskrift

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T1 - Three semidominant barley mutants with single amino acid substitutions in the smallest magnesium chelatase subunit form defective AAA+ hexamers

AU - Hansson, Andreas

AU - Willows, R D

AU - Roberts, T H

AU - Hansson, Mats

PY - 2002

Y1 - 2002

N2 - Many enzymes of the bacteriochlorophyll and chlorophyll biosynthesis pathways have been conserved throughout evolution, but the molecular mechanisms of the key steps remain unclear. The magnesium chelatase reaction is one of these steps, and it requires the proteins BchI, BchD, and BchH to catalyze the insertion of Mg2+ into protoporphyrin IX upon ATP hydrolysis. Structural analyses have shown that BchI forms hexamers and belongs to the ATPases associated with various cellular activities (AAA+) family of proteins. AAA+ proteins are Mg2+-dependent ATPases that normally form oligomeric ring structures in the presence of ATP. By using ATPase-deficient BchI subunits, we demonstrate that binding of ATP is sufficient to form BchI oligomers. Further, ATPase-deficient BchI proteins can form mixed oligomers with WT BchI. The formation of BchI oligomers is not sufficient for magnesium chelatase activity when combined with BchD and BchH. Combining WT BchI with ATPase-deficient BchI in an assay disrupts the chelatase reaction, but the presence of deficient BchI does not inhibit ATPase activity of the WT BchI. Thus, the ATPase of every WT segment of the hexamer is autonomous, but all segments of the hexamer must be capable of ATP hydrolysis for magnesium chelatase activity. We suggest that ATP hydrolysis of each BchI within the hexamer causes a conformational change of the hexamer as a whole. However, hexamers containing ATPase-deficient BchI are unable to perform this ATP-dependent conformational change, and the magnesium chelatase reaction is stalled in an early stage.

AB - Many enzymes of the bacteriochlorophyll and chlorophyll biosynthesis pathways have been conserved throughout evolution, but the molecular mechanisms of the key steps remain unclear. The magnesium chelatase reaction is one of these steps, and it requires the proteins BchI, BchD, and BchH to catalyze the insertion of Mg2+ into protoporphyrin IX upon ATP hydrolysis. Structural analyses have shown that BchI forms hexamers and belongs to the ATPases associated with various cellular activities (AAA+) family of proteins. AAA+ proteins are Mg2+-dependent ATPases that normally form oligomeric ring structures in the presence of ATP. By using ATPase-deficient BchI subunits, we demonstrate that binding of ATP is sufficient to form BchI oligomers. Further, ATPase-deficient BchI proteins can form mixed oligomers with WT BchI. The formation of BchI oligomers is not sufficient for magnesium chelatase activity when combined with BchD and BchH. Combining WT BchI with ATPase-deficient BchI in an assay disrupts the chelatase reaction, but the presence of deficient BchI does not inhibit ATPase activity of the WT BchI. Thus, the ATPase of every WT segment of the hexamer is autonomous, but all segments of the hexamer must be capable of ATP hydrolysis for magnesium chelatase activity. We suggest that ATP hydrolysis of each BchI within the hexamer causes a conformational change of the hexamer as a whole. However, hexamers containing ATPase-deficient BchI are unable to perform this ATP-dependent conformational change, and the magnesium chelatase reaction is stalled in an early stage.

U2 - 10.1073/pnas.212504499

DO - 10.1073/pnas.212504499

M3 - Article

VL - 99

SP - 13944

EP - 13949

JO - Proceedings of the National Academy of Sciences

JF - Proceedings of the National Academy of Sciences

SN - 1091-6490

IS - 21

ER -