cd06238, M14-like, Peptidase M14-like domain; uncharacterized subgroup. Peptidase M14-like domain of a functionally uncharacterized subgroup of the M14 family of metallocarboxypeptidases (MCPs). The M14 family are zinc-binding carboxypeptidases (CPs) which hydrolyze single, C-terminal amino acids from polypeptide chains, and have a recognition site for the free C-terminal carboxyl group, which is a key determinant of specificity. Two major subfamilies of the M14 family, defined based on sequence and structural homology, are the A/B and N/E subfamilies. Enzymes belonging to the A/B subfamily are normally synthesized as inactive precursors containing preceding signal peptide, followed by an N-terminal pro-region linked to the enzyme; these proenzymes are called procarboxypeptidases. The A/B enzymes can be further divided based on their substrate specificity; Carboxypeptidase A-like (CPA-like) enzymes favor hydrophobic residues while carboxypeptidase B-like (CPB-like) enzymes only cleave the basic residues lysine or arginine. The A forms have slightly different specificities, with Carboxypeptidase A1 (CPA1) preferring aliphatic and small aromatic residues, and CPA2 preferring the bulky aromatic side chains. Enzymes belonging to the N/E subfamily enzymes are not produced as inactive precursors and instead rely on their substrate specificity and subcellular compartmentalization to prevent inappropriate cleavage. They contain an extra C-terminal transthyretin-like domain, thought to be involved in folding or formation of oligomers. MCPs can also be classified based on their involvement in specific physiological processes; the pancreatic MCPs participate only in alimentary digestion and include carboxypeptidase A and B (A/B subfamily), while others, namely regulatory MCPs or the N/E subfamily, are involved in more selective reactions, mainly in non-digestive tissues and fluids, acting on blood coagulation/fibrinolysis, inflammation and local anaphylaxis, pro-hormone and neuropeptide processing, cellular response and others. Another MCP subfamily, is that of succinylglutamate desuccinylase /aspartoacylase, which hydrolyzes N-acetyl-L-aspartate (NAA), and deficiency in which is the established cause of Canavan disease. Another subfamily (referred to as subfamily C) includes an exceptional type of activity in the MCP family, that of dipeptidyl-peptidase activity of gamma-glutamyl-(L)-meso-diaminopimelate peptidase I which is involved in bacterial cell wall metabolism.
pfam12118, SprA-related, SprA-related family. This family of bacterial proteins has a conserved HEXXH motif, suggesting they are putative peptidases of zincin fold. Proteins in this family are typically between 234 to 465 amino acids in length. Most members are annotated as being SprA-related.
cd00085, HNHc, HNH nucleases; HNH endonuclease signature which is found in viral, prokaryotic, and eukaryotic proteins. The alignment includes members of the large group of homing endonucleases, yeast intron 1 protein, MutS, as well as bacterial colicins, pyocins, and anaredoxins.
pfam12256, TcdB_toxin_midN, Insecticide toxin TcdB middle/N-terminal region. This domain family is found in bacteria and archaea, and is typically between 164 and 180 amino acids in length. The family is found in association with pfam05593. This family is the N-terminal-sided middle region of the bacterial insecticide toxin TcdB. This region appears related to the FG-GAP repeat pfam01839.
pfam13618, Gluconate_2-dh3, Gluconate 2-dehydrogenase subunit 3. This family corresponds to subunit 3 of the Gluconate 2-dehydrogenase enzyme that catalyzes the conversion of gluconate to 2-dehydro-D-gluconate EC:1.1.99.3.
TIGR01738, Pimeloyl-_methyl_ester_esterase, pimelyl-[acyl-carrier protein] methyl ester esterase. This CoA-binding enzyme is required for the production of pimeloyl-coenzyme A, the substrate of the BioF protein early in the biosynthesis of biotin. Its exact function is unknown, but is proposed in ref 2. This enzyme belongs to the alpha/beta hydrolase fold family (pfam00561). Members of this family are restricted to the Proteobacteria. [Biosynthesis of cofactors, prosthetic groups, and carriers, Biotin].
pfam13899, Thioredoxin_7, Thioredoxin-like. Thioredoxins are small enzymes that participate in redox reactions, via the reversible oxidation of an active centre disulfide bond.
cd13831, HU, histone-like DNA-binding protein HU. This subfamily includes HU and HU-like domains. HU is a conserved nucleoid-associated protein (NAP) which binds non-specifically to duplex DNA with a particular preference for targeting nicked and bent DNA. It is highly basic and contributes to chromosomal compaction and maintenance of negative supercoiling, thus often referred to as histone-like protein. HU can induce DNA bends, condense DNA in a fiber and also interact with single stranded DNA. It contains two homologous subunits, alpha and beta, typically forming homodimers (alpha-alpha and beta-beta), except in E. coli and other enterobacteria, which form heterodimers (alpha-beta). In E. coli, HU binds uniformly to the chromosome, with a preference for damaged or distorted DNA structures and can introduce negative supercoils into closed circular DNA in the presence of topoisomerase I. Anabaena HU (AHU) shows preference for A/T-rich region in the center of its DNA binding site.
pfam05960, DUF885, Bacterial protein of unknown function (DUF885). This family consists of several hypothetical bacterial proteins several of which are putative membrane proteins.
TIGR03145, cyt_nit_nrfE, cytochrome c nitrate reductase biogenesis protein NrfE. Members of this protein family closely resemble the CcmF protein of the CcmABCDEFGH system, or system I, for c-type cytochrome biogenesis (GenProp0678). Members are found, as a rule, next to closely related paralogs of CcmG and CcmH and always located near other genes associated with the cytochrome c nitrite reductase enzyme complex. As a rule, members are found in species that also encode bona fide members of the CcmF, CcmG, and CcmH families.
cd06193, siderophore_interacting, Siderophore interacting proteins share the domain structure of the ferredoxin reductase like family. Siderophores are produced in various bacteria (and some plants) to extract iron from hosts. Binding constants are high, so iron can be pilfered from transferrin and lactoferrin for bacterial uptake, contributing to pathogen virulence. Ferredoxin reductase (FNR), an FAD and NAD(P) binding protein, was intially identified as a chloroplast reductase activity, catalyzing the electron transfer from reduced iron-sulfur protein ferredoxin to NADP+ as the final step in the electron transport mechanism of photosystem I. FNR transfers electrons from reduced ferredoxin to FAD (forming FADH2 via a semiquinone intermediate) and then transfers a hydride ion to convert NADP+ to NADPH. FNR has since been shown to utilize a variety of electron acceptors and donors and has a variety of physiological functions including nitrogen assimilation, dinitrogen fixation, steroid hydroxylation, fatty acid metabolism, oxygenase activity, and methane assimilation in a variety of organisms. FNR has an NAD(P)-binding sub-domain of the alpha/beta class and a discrete (usually N-terminal) flavin sub-domain which vary in orientation with respect to the NAD(P) binding domain. The N-terminal moeity may contain a flavin prosthetic group (as in flavoenzymes) or use flavin as a substrate. Because flavins such as FAD can exist in oxidized, semiquinone (one-electron reduced), or fully reduced hydroquinone forms, FNR can interact with one and two electron carriers. FNR has a strong preference for NADP(H) vs NAD(H).
cd03010, TlpA_like_DsbE, TlpA-like family, DsbE (also known as CcmG and CycY) subfamily; DsbE is a membrane-anchored, periplasmic TRX-like reductase containing a CXXC motif that specifically donates reducing equivalents to apocytochrome c via CcmH, another cytochrome c maturation (Ccm) factor with a redox active CXXC motif. Assembly of cytochrome c requires the ligation of heme to reduced thiols of the apocytochrome. In bacteria, this assembly occurs in the periplasm. The reductase activity of DsbE in the oxidizing environment of the periplasm is crucial in the maturation of cytochrome c.
cd08422, PBP2_CrgA_like, The C-terminal substrate binding domain of LysR-type transcriptional regulator CrgA and its related homologs, contains the type 2 periplasmic binding domain. This CD includes the substrate binding domain of LysR-type transcriptional regulator (LTTR) CrgA and its related homologs. The LTTRs are acting as both auto-repressors and activators of target promoters, controlling operons involved in a wide variety of cellular processes such as amino acid biosynthesis, CO2 fixation, antibiotic resistance, degradation of aromatic compounds, nodule formation of nitrogen-fixing bacteria, and synthesis of virulence factors, to name a few. In contrast to the tetrameric form of other LTTRs, CrgA from Neisseria meningitides assembles into an octameric ring, which can bind up to four 63-bp DNA oligonucleotides. Phylogenetic cluster analysis further showed that the CrgA-like regulators form a subclass of the LTTRs that function as octamers. The CrgA is an auto-repressor of its own gene and activates the expression of the mdaB gene which coding for an NADPH-quinone reductase and that its action is increased by MBL (alpha-methylene-gamma-butyrolactone), an inducer of NADPH-quinone oxidoreductase. The structural topology of this substrate-binding domain is most similar to that of the type 2 periplasmic binding proteins (PBP2), which are responsible for the uptake of a variety of substrates such as phosphate, sulfate, polysaccharides, lysine/arginine/ornithine, and histidine. The PBP2 bind their ligand in the cleft between these domains in a manner resembling a Venus flytrap. After binding their specific ligand with high affinity, they can interact with a cognate membrane transport complex comprised of two integral membrane domains and two cytoplasmically located ATPase domains. This interaction triggers the ligand translocation across the cytoplasmic membrane energized by ATP hydrolysis.
TIGR01451, unnamed_protein_product, conserved repeat domain. This model represents the conserved region of about 53 amino acids shared between regions, usually repeated, of proteins from a small number of phylogenetically distant prokaryotes. Examples include a 132-residue region found repeated in three of the five longest proteins of Bacillus anthracis, a 131-residue repeat in a cell wall-anchored protein of Enterococcus faecalis, and a 120-residue repeat in Methanobacterium thermoautotrophicum. A similar region is found in some Chlamydial outer membrane proteins.
pfam13387, DUF4105, Domain of unknown function (DUF4105). This is a family of uncharacterized bacterial proteins. There is a highly conserved histidine residue and a well-conserved NCT motif.
pfam01345, DUF11, Domain of unknown function DUF11. A domain of unknown function found in multiple copies in several archaebacterial proteins. Conserved N-terminal lysine and C-terminal asparagine with central asp/glu suggests that many of these domain may contain an isopeptide bond.
pfam00930, DPPIV_N, Dipeptidyl peptidase IV (DPP IV) N-terminal region. This family is an alignment of the region to the N-terminal side of the active site. The Prosite motif does not correspond to this Pfam entry.
cd13704, PBP2_HisK, The periplasmic sensor domain of histidine kinase receptors; the type 2 periplasmic binding fold protein. This subfamily includes the periplasmic sensor domain of the histidine kinase receptors (HisK) which are elements of the two-component signal transduction systems commonly found in bacteria and lower eukaryotes. Typically, the two-component system consists of a membrane-spanning histidine kinase sensor and a cytoplasmic response regulator. The two-component systems serve as a stimulus-response coupling mechanism to enable microorganisms to sense and respond to changes in environmental conditions. Extracellular stimuli such as small molecule ligands and ions are detected by the N-terminal periplasmic sensing domain of the sensor kinase receptor, which regulate the catalytic activity of the cytoplasmic kinase domain and promote ATP-dependent autophosphorylation of a conserved histidine residue. The phosphate is then transferred to a conserved aspartate in the response regulator through a phospho-transfer mechanism, and the activity of the response regulator is in turn regulated. The sensor domain belongs to the type 2 periplasmic-binding fold protein (PBP2) superfamily, whose members are involved in chemotaxis and uptake of nutrients and other small molecules from the extracellular space through their function as an initial high-affinity binding component. PBP2 typically comprises of two globular subdomains connected by a flexible hinge and bind their ligand in the cleft between these domains in a manner resembling a Venus flytrap.
