Annotations: 1AOP

Domain Annotation: SCOP/SCOPe Classification SCOP-e Database Homepage

Chains	Domain Info	Class	Fold	Superfamily	Family	Domain	Species	Provenance Source (Version)
A	d1aopa1	Alpha and beta proteins (a+b)	Ferredoxin-like	Nitrite/Sulfite reductase N-terminal domain-like	Duplicated SiR/NiR-like domains 1 and 3	Sulfite reductase, domains 1 and 3	(Escherichia coli B ) [TaxId: 37762 ],	SCOPe (2.08)
A	d1aopa3	Alpha and beta proteins (a+b)	Nitrite and sulphite reductase 4Fe-4S domain-like	Nitrite and sulphite reductase 4Fe-4S domain-like	Nitrite and sulphite reductase 4Fe-4S domain-like	Sulfite reductase hemoprotein (SiRHP), domains 2 and 4	(Escherichia coli B ) [TaxId: 37762 ],	SCOPe (2.08)

Domain Annotation: SCOP2 Classification SCOP2 Database Homepage

Chains	Type	Family Name	Domain Identifier	Family Identifier	Provenance Source (Version)
A	SCOP2B Superfamily	Nitrite and sulphite reductase 4Fe-4S domain-like	8036473	3000646	SCOP2B (2022-06-29)
A	SCOP2B Superfamily	Nitrite/Sulfite reductase N-terminal domain-like	8035688	3001366	SCOP2B (2022-06-29)
A	SCOP2B Superfamily	Nitrite/Sulfite reductase N-terminal domain-like	8035690	3001366	SCOP2B (2022-06-29)
A	SCOP2B Superfamily	Nitrite and sulphite reductase 4Fe-4S domain-like	8036474	3000646	SCOP2B (2022-06-29)

Domain Annotation: ECOD Classification ECOD Database Homepage

Chains	Family Name	Domain Identifier	Architecture	Possible Homology	Homology	Topology	Family	Provenance Source (Version)
A	NIR_SIR_ferr	e1aopA1	A: a+b two layers	X: Alpha-beta plaits	H: Sulfite reductase, domains 1 and 3 (From Topology)	T: Sulfite reductase, domains 1 and 3	F: NIR_SIR_ferr	ECOD (1.6)
A	NIR_SIR	e1aopA3	A: a+b three layers	X: Sulfite reductase hemoprotein (SiRHP), domains 2 and 4 (From Topology)	H: Sulfite reductase hemoprotein (SiRHP), domains 2 and 4 (From Topology)	T: Sulfite reductase hemoprotein (SiRHP), domains 2 and 4	F: NIR_SIR	ECOD (1.6)

Domain Annotation: CATH CATH Database Homepage

Chain	Domain	Class	Architecture	Topology	Homology	Provenance Source (Version)
A	3.30.413.10	Alpha Beta	2-Layer Sandwich	Sulfite Reductase Hemoprotein	domain 1	CATH (4.3.0)
A	3.90.480.10	Alpha Beta	Alpha-Beta Complex	Sulfite Reductase Hemoprotein	domain 2	CATH (4.3.0)

Protein Family Annotation Pfam Database Homepage

Chains	Accession	Name	Description	Comments	Source
A	PF03460	Nitrite/Sulfite reductase ferredoxin-like half domain (NIR_SIR_ferr)	Nitrite/Sulfite reductase ferredoxin-like half domain	-	Repeat
A	PF01077	Nitrite and sulphite reductase 4Fe-4S domain (NIR_SIR)	Nitrite and sulphite reductase 4Fe-4S domain	-	Family

Gene Ontology: Gene Product Annotation Gene Ontology Database Homepage

Chains	Polymer	Molecular Function	Biological Process	Cellular Component
A	SULFITE REDUCTASE HEMOPROTEIN	oxidoreductase activity, acting on a sulfur group of donors sulfite reductase (NADPH) activity oxidoreductase activity sulfite reductase activity catalytic activity oxidoreductase activity, acting on a sulfur group of donors, NAD(P) as acceptor binding nucleoside phosphate binding purine nucleotide binding adenyl nucleotide binding nucleotide binding heterocyclic compound binding NADP binding small molecule binding oxidoreductase activity, acting on a sulfur group of donors sulfite reductase (NADPH) activity oxidoreductase activity sulfite reductase activity catalytic activity oxidoreductase activity, acting on a sulfur group of donors, NAD(P) as acceptor binding nucleoside phosphate binding purine nucleotide binding adenyl nucleotide binding nucleotide binding heterocyclic compound binding NADP binding small molecule binding tetrapyrrole binding heme binding oxidoreductase activity, acting on a sulfur group of donors, iron-sulfur protein as acceptor sulfite reductase (ferredoxin) activity iron-sulfur cluster binding 4 iron, 4 sulfur cluster binding metal cluster binding cation binding ion binding metal ion binding	sulfur compound biosynthetic process biosynthetic process sulfur compound metabolic process metabolic process cellular process hydrogen sulfide biosynthetic process hydrogen sulfide metabolic process serine family amino acid metabolic process oxoacid metabolic process sulfur amino acid metabolic process amino acid metabolic process organic acid biosynthetic process organic acid metabolic process alpha-amino acid metabolic process sulfur compound biosynthetic process biosynthetic process sulfur compound metabolic process metabolic process cellular process hydrogen sulfide biosynthetic process hydrogen sulfide metabolic process serine family amino acid metabolic process oxoacid metabolic process sulfur amino acid metabolic process amino acid metabolic process organic acid biosynthetic process organic acid metabolic process alpha-amino acid metabolic process carboxylic acid biosynthetic process cysteine biosynthetic process small molecule metabolic process small molecule biosynthetic process carboxylic acid metabolic process primary metabolic process cysteine metabolic process amino acid biosynthetic process serine family amino acid biosynthetic process sulfur amino acid biosynthetic process alpha-amino acid biosynthetic process sulfate assimilation	protein-containing complex catalytic complex sulfite reductase complex (NADPH) intracellular protein-containing complex

InterPro: Protein Family Classification InterPro Database Homepage

Chains	Accession	Name	Type
A	IPR011786	Sulphite reductase (NADPH) hemoprotein, beta subunit	Family
A	IPR005117	Nitrite/Sulfite reductase ferredoxin-like domain	Domain
A	IPR006067	Nitrite/sulphite reductase 4Fe-4S domain	Domain
A	IPR006066	Nitrite/sulphite reductase iron-sulphur/sirohaem-binding site	Binding Site
A	IPR045854	Nitrite and sulphite reductase 4Fe-4S domain-like superfamily	Homologous Superfamily
A	IPR036136	Nitrite/Sulfite reductase ferredoxin-like domain superfamily	Homologous Superfamily
A	IPR045169	Nitrite and sulphite reductase 4Fe-4S domain containing protein	Family

Structure Motif Annotation: Mechanism and Catalytic Site Atlas M-CSA Database Homepage

Chains	Enzyme Name	Description	Catalytic Residues
A	sulfite reductase (NADPH) M-CSA #398	The E. coli enzyme sulphite reductase, SiR, is a multimeric hemoflavoprotein that catalyses the six-electron reduction of sulphite (SO₃^-) to sulphide (HS^-) and of nitrite (NO₂^-) to ammonia (NH₄⁺) using electrons from NADPH. The complex consists of two types of subunit: the flavoprotein SiRFP and the hemoprotein SiRHP. Recent studies have suggested that the complex contains 8 subunits of SiRFP and 8 of SiRHP, rather than 8 of SiRFP and 4 of SiRHP as previously assumed. Electrons are transferred from NADPH to FAD in SiRFP and then to FMN in SiRFP. Next they are transferred to a 4Fe4S centre in SiRHP, which is linked to a sirohaem via a common cysteine ligand. Electrons are ultimately transferred to the substrate that is coordinated to the sirohaem iron. This entry deals only with the SiRHP component of the complex.	Defined by 8 residues: ARG:A-10 [auth A-83]ARG:A-80 [auth A-153]LYS:A-142 [auth A-215]LYS:A-144 [auth A-217]CYS:A-361 [auth A-434]CYS:A-367 [auth A-440]CYS:A-406 [auth A-479]CYS:A-410 [auth A-483] \| Explore in 3D: M-CSA Motif Definition Search M-CSA Motif EC: 1.8.1.2 (PDB Primary Data) Search M-CSA Motif + EC 1.8.1.2

RCSB PDB Core Operations are funded by the U.S. National Science Foundation (DBI-2321666), the US Department of Energy (DE-SC0019749), and the National Cancer Institute, National Institute of Allergy and Infectious Diseases, and National Institute of General Medical Sciences of the National Institutes of Health under grant R01GM157729.