|Gene:||hscA||Accession Numbers: EG12130 (EcoCyc), b2526, ECK2523|
Synonyms: hsc, Hsc66, chaperone, member of Hsp70 protein family
HscA together with HscB comprises a chaperone/cochaperone system similar to DnaK/DnaJ [Vickery97, Silberg98]. HscA is required for the assembly of iron-sulfur clusters [Takahashi99, Tokumoto01]. Models for chaperone-facilitated Fe-S cluster transfer have been proposed. One model involves an exchange of Fe-S cluster ligands in the iron-sulfur cluster scaffold protein IscU upon chaperone binding that facilitates cluster transfer [Bonomi11]; another involves chaperone-mediated disordering of IscU that promotes the transfer of the Fe-S cluster to an acceptor protein [Kim12a].
HscA consists of two domains, a nucleotide-binding domain (NBD) that binds and hydrolyzes ATP [Vickery97] and a substrate-binding domain that binds IscU [Silberg01]. The inter-domain linker peptide is able to stimulate the rate of ATP hydrolysis of the isolated NBD [Alderson14].
Under steady-state conditions, ATP hydrolysis rather than ADP/ATP nucleotide exchange is the rate-limiting step in the HscA reaction cycle [Silberg00]; the dissociation rates for ATP and ADP are comparatively fast [Brehmer01]. IscU is a substrate for HscA [Silberg01]; in the presence of HscB, IscU stimulates the ATPase activity of HscA up to 480-fold [Hoff00, Hoff03]. The in vivo turnover rate of the chaperone cycle may be determined by the availability of the IscU-HscB complex [Silberg04]. In the presence of HscA and HscB, conformational changes in the [2Fe-2S] cluster of IscU appear to be coupled to ATP hydrolysis by HscA [Bonomi08]. Interaction of HscA with IscU occurs via the LPPVK sequence motif in IscU, is highly directional [Hoff02, Hoff03, Tapley04], and occurs in both the ATP- and ADP-bound state, while interaction with HscB occurs primarily in the ATP-bound state [Silberg04, Kim14b]. HscA alone or in the ADP-bound state preferentially binds to and stabilizes the dynamically disordered state of IscU. Binding of ATP leads to release of IscU [Kim12a].
HscA interacts with the apo form of biotin synthase and improves the efficiency of the assembly of the [2Fe-2S] cluster on the enzyme, which is thought to provide the sulfur atom in the biotin synthase reaction. The HscA-BioB complex also binds IscU [Reyda09].
A crystal structure of the HscA substrate binding domain in complex with the IscU recognition peptide has been reported [CuppVickery04]. The sequence requirements for recognition of IscU by HscA have been explored by site-directed mutagenesis [Tapley06].
Expression of hscA is induced by cold shock, but not by heat shock [Lelivelt95]. An hscA mutant does not have a general protein folding defect, and overproduction of HscA does not complement a ΔdnaK52 mutant [Hesterkamp98]. An hscA mutant has increased doubling time in rich media and has lower activity of the Fe-S enzymes GltS and SDH than wild type [Tokumoto01].
Gene Citations: [Tokumoto02]
|Map Position: [2,655,107 <- 2,656,957] (57.23 centisomes, 206°)||Length: 1851 bp / 616 aa|
Molecular Weight of Polypeptide: 65.652 kD (from nucleotide sequence), 62.0 kD (experimental) [Vickery97 ]
Unification Links: ASAP:ABE-0008315 , CGSC:32977 , DIP:DIP-47348N , EchoBASE:EB2051 , EcoGene:EG12130 , EcoliWiki:b2526 , ModBase:P0A6Z1 , OU-Microarray:b2526 , PortEco:hscA , PR:PRO_000022925 , Pride:P0A6Z1 , Protein Model Portal:P0A6Z1 , RefSeq:NP_417021 , RegulonDB:EG12130 , SMR:P0A6Z1 , String:511145.b2526 , Swiss-Model:P0A6Z1 , UniProt:P0A6Z1
Relationship Links: InterPro:IN-FAMILY:IPR010236 , InterPro:IN-FAMILY:IPR013126 , InterPro:IN-FAMILY:IPR018181 , InterPro:IN-FAMILY:IPR029047 , InterPro:IN-FAMILY:IPR029048 , PDB:Structure:1U00 , Pfam:IN-FAMILY:PF00012 , Prints:IN-FAMILY:PR00301 , Prosite:IN-FAMILY:PS00297 , Prosite:IN-FAMILY:PS00329 , Prosite:IN-FAMILY:PS01036
In Paralogous Gene Group: 5 (5 members)
|Biological Process:||GO:0070417 - cellular response to cold
GO:0097428 - protein maturation by iron-sulfur cluster transfer [Bonomi08, Takahashi99]
GO:0006457 - protein folding [GOA06, GOA01a]
GO:0016226 - iron-sulfur cluster assembly [GOA01a]
|Molecular Function:||GO:0005515 - protein binding
[Reyda09, Tokumoto02, Silberg04, Hoff03]
GO:0005524 - ATP binding [UniProtGOA11a, GOA01a, Brehmer01, Silberg00]
GO:0016887 - ATPase activity [GOA06, GOA01a, Silberg00]
GO:0043531 - ADP binding [Brehmer01]
GO:0000166 - nucleotide binding [UniProtGOA11a]
GO:0051082 - unfolded protein binding [GOA01a]
|Cellular Component:||GO:0005829 - cytosol
GO:1990230 - iron-sulfur cluster transfer complex [Bonomi08]
|MultiFun Terms:||information transfer → protein related → chaperoning, repair (refolding)|
|Growth Medium||Growth?||T (°C)||O2||pH||Osm/L||Growth Observations|
|LB Lennox||Yes||37||Aerobic||7||Yes [Baba06, Comment 1]|
|M9 medium with 1% glycerol||Yes||37||Aerobic||7.2||0.35||Yes [Joyce06, Comment 2]|
|MOPS medium with 0.4% glucose||Yes||37||Aerobic||7.2||0.22||Yes [Baba06, Comment 1]|
Enzymatic reaction of: non-chaperonin molecular chaperone ATPase (chaperone for [Fe-S] cluster biosynthesis)
EC Number: 3.6.4.-
The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction of enzyme catalysis.
The reaction is physiologically favored in the direction shown. [Silberg00]
|Sequence-Conflict||456 -> 465|
10/20/97 Gene b2526 from Blattner lab Genbank (v. M52) entry merged into EcoCyc gene EG12130; confirmed by SwissProt match.
Alderson14: Alderson TR, Kim JH, Cai K, Frederick RO, Tonelli M, Markley JL (2014). "Specialized Hsp70 (HscA) interdomain linker binds to its nucleotide-binding domain and stimulates ATP hydrolysis in both cis and trans configurations." Biochemistry. PMID: 25372495
Aoto05: Aoto PC, Ta DT, Cupp-Vickery JR, Vickery LE (2005). "X-ray diffraction analysis of a crystal of HscA from Escherichia coli." Acta Crystallogr Sect F Struct Biol Cryst Commun 61(Pt 7);715-7. PMID: 16511138
Baba06: Baba T, Ara T, Hasegawa M, Takai Y, Okumura Y, Baba M, Datsenko KA, Tomita M, Wanner BL, Mori H (2006). "Construction of Escherichia coli K-12 in-frame, single-gene knockout mutants: the Keio collection." Mol Syst Biol 2;2006.0008. PMID: 16738554
Bonomi08: Bonomi F, Iametti S, Morleo A, Ta D, Vickery LE (2008). "Studies on the mechanism of catalysis of iron-sulfur cluster transfer from IscU[2Fe2S] by HscA/HscB chaperones." Biochemistry 47(48);12795-801. PMID: 18986169
Brehmer01: Brehmer D, Rudiger S, Gassler CS, Klostermeier D, Packschies L, Reinstein J, Mayer MP, Bukau B (2001). "Tuning of chaperone activity of Hsp70 proteins by modulation of nucleotide exchange." Nat Struct Biol 8(5);427-32. PMID: 11323718
CuppVickery04: Cupp-Vickery JR, Peterson JC, Ta DT, Vickery LE (2004). "Crystal structure of the molecular chaperone HscA substrate binding domain complexed with the IscU recognition peptide ELPPVKIHC." J Mol Biol 342(4);1265-78. PMID: 15351650
DiazMejia09: Diaz-Mejia JJ, Babu M, Emili A (2009). "Computational and experimental approaches to chart the Escherichia coli cell-envelope-associated proteome and interactome." FEMS Microbiol Rev 33(1);66-97. PMID: 19054114
Genevaux07: Genevaux P, Georgopoulos C, Kelley WL (2007). "The Hsp70 chaperone machines of Escherichia coli: a paradigm for the repartition of chaperone functions." Mol Microbiol 66(4);840-57. PMID: 17919282
Hoff00: Hoff KG, Silberg JJ, Vickery LE (2000). "Interaction of the iron-sulfur cluster assembly protein IscU with the Hsc66/Hsc20 molecular chaperone system of Escherichia coli." Proc Natl Acad Sci U S A 97(14);7790-5. PMID: 10869428
Hoff02: Hoff KG, Ta DT, Tapley TL, Silberg JJ, Vickery LE (2002). "Hsc66 substrate specificity is directed toward a discrete region of the iron-sulfur cluster template protein IscU." J Biol Chem 277(30);27353-9. PMID: 11994302
Hoff03: Hoff KG, Cupp-Vickery JR, Vickery LE (2003). "Contributions of the LPPVK motif of the iron-sulfur template protein IscU to interactions with the Hsc66-Hsc20 chaperone system." J Biol Chem 278(39):37582-9. PMID: 12871959
Joyce06: Joyce AR, Reed JL, White A, Edwards R, Osterman A, Baba T, Mori H, Lesely SA, Palsson BO, Agarwalla S (2006). "Experimental and computational assessment of conditionally essential genes in Escherichia coli." J Bacteriol 188(23);8259-71. PMID: 17012394
Kawula94: Kawula TH, Lelivelt MJ (1994). "Mutations in a gene encoding a new Hsp70 suppress rapid DNA inversion and bgl activation, but not proU derepression, in hns-1 mutant Escherichia coli." J Bacteriol 176(3);610-9. PMID: 8300516
Kim12a: Kim JH, Tonelli M, Frederick RO, Chow DC, Markley JL (2012). "Specialized Hsp70 chaperone (HscA) binds preferentially to the disordered form, whereas J-protein (HscB) binds preferentially to the structured form of the iron-sulfur cluster scaffold protein (IscU)." J Biol Chem 287(37);31406-13. PMID: 22782893
Kim14b: Kim JH, Alderson TR, Frederick RO, Markley JL (2014). "Nucleotide-dependent interactions within a specialized Hsp70/Hsp40 complex involved in Fe-S cluster biogenesis." J Am Chem Soc 136(33);11586-9. PMID: 25080945
Markley13: Markley JL, Kim JH, Dai Z, Bothe JR, Cai K, Frederick RO, Tonelli M (2013). "Metamorphic protein IscU alternates conformations in the course of its role as the scaffold protein for iron-sulfur cluster biosynthesis and delivery." FEBS Lett. PMID: 23333622
Reyda09: Reyda MR, Fugate CJ, Jarrett JT (2009). "A complex between biotin synthase and the iron-sulfur cluster assembly chaperone HscA that enhances in vivo cluster assembly." Biochemistry 48(45);10782-92. PMID: 19821612
Roche13: Roche B, Aussel L, Ezraty B, Mandin P, Py B, Barras F (2013). "Reprint of: Iron/sulfur proteins biogenesis in prokaryotes: formation, regulation and diversity." Biochim Biophys Acta 1827(8-9);923-37. PMID: 23660107
Silberg01: Silberg JJ, Hoff KG, Tapley TL, Vickery LE (2001). "The Fe/S assembly protein IscU behaves as a substrate for the molecular chaperone Hsc66 from Escherichia coli." J Biol Chem 276(3);1696-700. PMID: 11053447
Silberg04: Silberg JJ, Tapley TL, Hoff KG, Vickery LE (2004). "Regulation of the HscA ATPase reaction cycle by the co-chaperone HscB and the iron-sulfur cluster assembly protein IscU." J Biol Chem 279(52):53924-31. PMID: 15485839
Silberg98: Silberg JJ, Hoff KG, Vickery LE (1998). "The Hsc66-Hsc20 chaperone system in Escherichia coli: chaperone activity and interactions with the DnaK-DnaJ-grpE system." J Bacteriol 180(24);6617-24. PMID: 9852006
Takahashi99: Takahashi Y, Nakamura M (1999). "Functional assignment of the ORF2-iscS-iscU-iscA-hscB-hscA-fdx-ORF3 gene cluster involved in the assembly of Fe-S clusters in Escherichia coli." J Biochem (Tokyo) 1999;126(5);917-26. PMID: 10544286
Tokumoto01: Tokumoto U, Takahashi Y (2001). "Genetic analysis of the isc operon in Escherichia coli involved in the biogenesis of cellular iron-sulfur proteins." J Biochem (Tokyo) 130(1);63-71. PMID: 11432781
Tokumoto02: Tokumoto U, Nomura S, Minami Y, Mihara H, Kato S, Kurihara T, Esaki N, Kanazawa H, Matsubara H, Takahashi Y (2002). "Network of protein-protein interactions among iron-sulfur cluster assembly proteins in Escherichia coli." J Biochem (Tokyo) 131(5);713-9. PMID: 11983079
Giel06: Giel JL, Rodionov D, Liu M, Blattner FR, Kiley PJ (2006). "IscR-dependent gene expression links iron-sulphur cluster assembly to the control of O-regulated genes in Escherichia coli." Mol Microbiol 60(4);1058-75. PMID: 16677314
Kaleta10: Kaleta C, Gohler A, Schuster S, Jahreis K, Guthke R, Nikolajewa S (2010). "Integrative inference of gene-regulatory networks in Escherichia coli using information theoretic concepts and sequence analysis." BMC Syst Biol 4;116. PMID: 20718955
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