Structural highlights
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Function
[ARNA_ECOLI] Bifunctional enzyme that catalyzes the oxidative decarboxylation of UDP-glucuronic acid (UDP-GlcUA) to UDP-4-keto-arabinose (UDP-Ara4O) and the addition of a formyl group to UDP-4-amino-4-deoxy-L-arabinose (UDP-L-Ara4N) to form UDP-L-4-formamido-arabinose (UDP-L-Ara4FN). The modified arabinose is attached to lipid A and is required for resistance to polymyxin and cationic antimicrobial peptides.[1] [2]
Publication Abstract from PubMed
The bacterial protein ArnA is an essential enzyme in the pathway leading to the modification of lipid A with the pentose sugar 4-amino-4-deoxy-L-arabinose. This modification confers resistance to polymyxins, which are antibiotics that are used as a last resort to treat infections with multiple drug-resistant Gram-negative bacteria. ArnA contains two domains with distinct catalytic functions: a dehydrogenase domain and a transformylase domain. The protein forms homohexamers organized as a dimer of trimers. Here, the crystal structure of apo ArnA is presented and compared with its ATP- and UDP-glucuronic acid-bound counterparts. The comparison reveals major structural rearrangements in the dehydrogenase domain that lead to the formation of a previously unobserved binding pocket at the centre of each ArnA trimer in its apo state. In the crystal structure, this pocket is occupied by a DTT molecule. It is shown that formation of the pocket is linked to a cascade of structural rearrangements that emerge from the NAD(+)-binding site. Based on these findings, a small effector molecule is postulated that binds to the central pocket and modulates the catalytic properties of ArnA. Furthermore, the discovered conformational changes provide a mechanistic explanation for the strong cooperative effect recently reported for the ArnA dehydrogenase function.
The structure of apo ArnA features an unexpected central binding pocket and provides an explanation for enzymatic cooperativity.,Fischer U, Hertlein S, Grimm C Acta Crystallogr D Biol Crystallogr. 2015 Mar;71(Pt 3):687-96. doi:, 10.1107/S1399004714026686. Epub 2015 Feb 26. PMID:25760615[3]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Breazeale SD, Ribeiro AA, Raetz CR. Oxidative decarboxylation of UDP-glucuronic acid in extracts of polymyxin-resistant Escherichia coli. Origin of lipid a species modified with 4-amino-4-deoxy-L-arabinose. J Biol Chem. 2002 Jan 25;277(4):2886-96. Epub 2001 Nov 8. PMID:11706007 doi:http://dx.doi.org/10.1074/jbc.M109377200
- ↑ Breazeale SD, Ribeiro AA, McClerren AL, Raetz CR. A formyltransferase required for polymyxin resistance in Escherichia coli and the modification of lipid A with 4-Amino-4-deoxy-L-arabinose. Identification and function oF UDP-4-deoxy-4-formamido-L-arabinose. J Biol Chem. 2005 Apr 8;280(14):14154-67. Epub 2005 Jan 28. PMID:15695810 doi:http://dx.doi.org/M414265200
- ↑ Fischer U, Hertlein S, Grimm C. The structure of apo ArnA features an unexpected central binding pocket and provides an explanation for enzymatic cooperativity. Acta Crystallogr D Biol Crystallogr. 2015 Mar;71(Pt 3):687-96. doi:, 10.1107/S1399004714026686. Epub 2015 Feb 26. PMID:25760615 doi:http://dx.doi.org/10.1107/S1399004714026686
