02446nas a2200385   4500000000100000008004100001260001600042653002400058653002300082653001800105653002300123653001600146653001200162653002200174653002800196653002500224653002500249653003400274653002200308653002600330100001200356700001400368700001500382700001400397700001400411700001700425700001600442700001300458700001400471245005600485300001200541490000800553520148500561022001402046       2002                            d  c2002 Jun 2810aAmino Acid Sequence10aBacterial Proteins10aBase Sequence10aCloning, Molecular10aHemoglobins10aLigands10aModels, Molecular10aMolecular Sequence Data10aMycobacterium leprae10aRecombinant Proteins10aSequence Homology, Amino Acid10aSpectrophotometry10aTruncated Hemoglobins1 aVisca P1 aFabozzi G1 aPetrucca A1 aCiaccio C1 aColetta M1 aDe Sanctis G1 aBolognesi M1 aMilani M1 aAscenzi P00aThe truncated hemoglobin from Mycobacterium leprae.  a1064-700 v2943 a<p>Truncated hemoglobins (trHb's) form a family of low molecular weight O2 binding hemoproteins distributed in eubacteria, protozoa, and plants. TrHb's branch in a distinct clade within the hemoglobin (Hb) superfamily. A unique globin gene has recently been identified from the complete genome sequence of Mycobacterium leprae that is predicted to encode a trHb (M. leprae trHbO). Sequence comparison and modelling considerations indicate that monomeric M. leprae trHbO has structural features typical of trHb's, such as 20-40 fewer residues than conventional globin chains, Gly-based sequence consensus motifs, likely assembling into a 2-on-2 alpha-helical sandwich fold, and hydrophobic residues recognized to build up the protein matrix ligand diffusion tunnel. The ferrous heme iron atom of deoxygenated M. leprae trHbO appears to be hexacoordinated, like in Arabidopsis thaliana trHbO-3 (A. thaliana trHbO-3). Accordingly, the value of the second-order rate constant for M. leprae trHbO carbonylation (7.3 x 10(3) M(-1) s(-1)) is similar to that observed for A. thaliana trHbO-3 (1.4 x 10(4) M(-1) s(-1)) and turns out to be lower than that reported for carbon monoxide binding to pentacoordinated Mycobacterium tuberculosis trHbN (6.7 x 10(6) M(-1) s(-1)). The lower reactivity of M. leprae trHbO as compared to M. tuberculosis trHbN might be related to the higher susceptibility of the leprosy bacillus to toxic nitrogen and oxygen species produced by phagocytic cells.</p>  a0006-291X