CupAR negatively controls the key protein CupA in the carbon acquisition complex NDH-1MS in Synechocystis sp. PCC 6803.

Abstract

The low CO2-inducible NDH complex (NDH-1MS) plays a crucial role in the cyanobacterial CO2-concentrating mechanism (CCM). However, the components in this complex and the regulation mechanism are still not completely understood. Using a mutant only with NDH-1MS as active Ci sequestration system, we identified a functional gene sll1736 named as cupAR (CupA Regulator). The cupAR deletion mutant, ΔcupAR, grew faster than the wild type (WT) under high CO2 (HC) condition, more evidently at low pH. The activities of O2 evolution, CO2 uptake，NDH-1 and the building up of a trans-thylakoid proton were stimulated in this mutant under HC conditions. The cupAR gene is co-transcribed with the NDH-1S operon (ndhF3-ndhD3-cupA) and encoded protein which specifically suppresses the transcription level of this operon under HC conditions. Mutation of cupAR significantly up-regulated the accumulation of CupA, the key protein of NDH-1MS, under HC condition. CupAR interacted with NdhD3 and NdhF3, the membrane components of NDH-1MS, while accumulation of CupAR was reduced in the ΔndhD3 mutant. Furthermore, CupAR was co-located with CupA in both NDH-1MS complex and NDH-1S subcomplex. On the other hand, deletion of ndhR, a negative regulator of the NDH-1S operon increased the accumulation of CupAR, while deletion of cupAR significantly lowered NdhR. Based on these results, we concluded that CupAR is a novel subunit of NDH-1MS, negatively regulating the activities of CupA and CO2 uptake dependent on NDH-1MS by positive regulation of NdhR under enriched CO2 conditions.