The NblAI protein from the filamentous cyanobacterium Tolypothrix PCC 7601: regulation of its expression and interactions with phycobilisome components

Abstract

SummaryCyanobacteria respond to changes in light or nutrient availability by modifications in their photosynthetic light harvesting antenna. In unicellular cyanobacteria a small polypeptide (NblA) is required for phycobilisome degradation following environmental stresses. In the filamentous strain Tolypothrix sp. PCC 7601 the nblAI gene, encoding a NblA homologue, is located upstream of the operon coding for phycoerythrin ( cpeBA ). The nblAI transcripts all originate from a single transcription start point; their intracellular levels vary according to nitrogen regimes but not with light spectral quality. Using recombinant His-tagged NblAI protein, we found that in vitro NblAI has affinity for both phycocyanin and phycoerythrin subunits from Tolypothrix sp. PCC 7601, but not for allophycocyanin from this cyanobacterium or for phycobiliproteins from other cyanobacterial species. We also observed that although nblAI is mainly expressed under nitrogen starvation, NblAI polypeptides are always present in the cell; a significant portion of them co-purify with phycobilisome preparations but only if cells were grown under red light. Our data indicate that NblAI attaches to the phycobilisomes even under non-inducing conditions and suggest a preferential affinity of NblAI for phycocyanin.

NblA, a Key Protein of Phycobilisome Degradation, Interacts with ClpC, a HSP100 Chaperone Partner of a Cyanobacterial Clp Protease

“…Although it has been shown that NblA binds to phycobiliproteins (22,25), the exact function of the NblA protein has not yet been elucidated. Here we provided evidence for an interaction between NblA and ClpC, suggesting that PBS degradation occurs via a Clp protease.…”

“…Sequence and structure of NblA show no significant similarity to proteins with known function, and the molecular mechanism of NblA action in PBS degradation is not clear. In vitro studies showed that NblA interacts with the ␣-subunits of phycobiliproteins (22,25). Furthermore, results of binding experiments with variants of NblA carrying amino acid substitutions at various positions provided evidence that the interaction with phycobiliproteins is mediated via conserved amino acid residues near its C terminus (25).…”

Immunolocalization of NblA, a protein involved in phycobilisome turnover, during heterocyst differentiation in cyanobacteria

“…In a recent study we have shown that this 15 kDa form -a dimer or a complex formed by NblAI and another small molecule -is always present, and that the~7 kDa form does exist but it is only found at such a molecular mass when associated with phycobiliproteins. Such a situation only occurs when cells are grown under red light, conditions under which both the 15 and 7 kDa proteins coexist (Luque et al, 2003). The NblAI increase observed in the three Tolypothrix sp.…”

“…Complete genomic sequences revealed that in some strains there may exist up to four nblA gene copies. Based on sequence similarities, the Tolypothrix PCC 7601 nblA gene that we have studied was designated nblAI (Luque et al, 2003), and this name will be used throughout. Anti-NblAI antibodies were raised and used to probe extracts from cells grown under nitrogendepleted and nitrogen-replete conditions.…”

Distinct light-, stress-, and nutrient-dependent regulation of multiple tryptophan-rich sensory protein (TSPO) genes in the cyanobacterium Fremyella diplosiphon

“…16 Therefore, the effect of changes in nitrogen availability on TSPO mRNA levels was assessed before and after exposing F. diplosiphon cells to changes in nitrogen availability (Fig. 5).…”