PMID:22081393

Citation	Pinske, C and Sawers, RG (2011) The A-type Carrier Protein ErpA is Essential for Formation of an Active Formate-Nitrate Respiratory Pathway in Escherichia coli K-12.J Bacteriol
Abstract	A-type carrier (ATC) proteins of the Isc (iron-sulfur-cluster) and Suf (sulfur mobilization) iron-sulfur ([Fe-S]) cluster biogenesis pathways are proposed to traffic pre-formed [Fe-S] clusters to apoprotein targets. In this study we analyzed the roles of the ATC proteins ErpA, IscA and SufA in the maturation of the nitrate-inducible, multi-subunit anaerobic respiratory enzymes formate dehydrogenase-N (Fdh-N) and nitrate reductase (Nar). Mutants lacking SufA had enhanced activities of both enzymes. While both Fdh-N and Nar activities were strongly reduced in an iscA mutant, both enzymes were inactive in an erpA mutant and in a mutant unable to synthesize the [Fe-S] cluster scaffold protein IscU. It could be shown for both Fdh-N and Nar that loss of enzyme activity correlated with absence of the [Fe-S] cluster-containing small subunit. Moreover, a slowly migrating form of the catalytic subunit FdnG of Fdh-N was observed, consistent with impeded TAT-dependent transport. The highly related Fdh-O enzyme was also inactive in the erpA mutant. Although the Nar enzyme has its catalytic subunit NarG localized in the cytoplasm, it also exhibited an aberrant migration in an erpAiscA mutant suggesting that these modular enzymes lack catalytic integrity due to impaired cofactor bioynthesis. Cross-complementation experiments demonstrated that multicopy IscA could partially compensate for lack of ErpA with respect to Fdh-N activity but not Nar activity. These findings suggest that ErpA and IscA have overlapping roles in assembly of these anaerobic respiratory enzymes but demonstrate that ErpA is essential for the production of active enzymes.
Links	PubMed Online version:10.1128/JB.06024-11
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Phenotype of	Taxon Information	Genotype Information (if known)	Condition Information	OMP ID	OMP Term Name	ECO ID	ECO Term Name	Notes	Status
a mutation or genetic difference within a strain	Taxon: Escherichia coli Strain: K-12 Substrain: LL402 NCBI Taxon ID: 83333	Genotype of Reference Strain: erpA Genotype of Experimental Strain : erpA(del)	Reference Condition:	OMP:0007185	decreased anaerobic respiration	ECO:0000016	loss-of-function mutant phenotype evidence	Deletion of erpA inactivates both Fdh-N and Nar enzymes, Table 2.
a mutation or genetic difference within a strain	Taxon: Escherichia coli Strain: K-12 Substrain: CP1223 NCBI Taxon ID: 83333	Genotype of Reference Strain: sufA Genotype of Experimental Strain : sufA(del)	Reference Condition:	OMP:0007184	increased anaerobic respiration	ECO:0000016	loss-of-function mutant phenotype evidence	The sufA(del) mutation increases activity of both Fdh-N and Nar-Table 2.
a mutation or genetic difference within a strain	Taxon: Escherichia coli Strain: K-12 Substrain: CP477 NCBI Taxon ID: 83333	Genotype of Reference Strain: IscA Genotype of Experimental Strain : IscA(del)	Reference Condition:	OMP:0007185	decreased anaerobic respiration	ECO:0000016	loss-of-function mutant phenotype evidence	Deletion of IscA strongly reduces activity of both Fdh-N and Nar enzymes-Table 2. Multicopy IscA could partially compensate for lack of ErpA with respect to Fdh-N activity but not Nar activity.
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