Conformation of the sebacyl β1Lys82–β2Lys82 crosslink in T-state human hemoglobin
✍ Scribed by Xinhua Ji; Michael Braxenthaler; John Moult; Clara Fronticelli; Enrico Bucci; Gary L. Gilliland
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 893 KB
- Volume
- 30
- Category
- Article
- ISSN
- 0887-3585
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✦ Synopsis
The crystal structure of human T state hemoglobin crosslinked with bis(3,5-dibromo-salicyl) sebacate has been determined at 1.9 Å resolution. The final crystallographic R factor is 0.168 with root-meansquare deviations (RMSD) from ideal bond distance of 0.018 Å. The 10-carbon sebacyl residue found in the  cleft covalently links the two Lys82 residues. The sebacyl residue assumes a zigzag conformation with cis amide bonds formed by the NZ atoms of Lys82's and the sebacyl carbonyl oxygens. The atoms of the crosslink have an occupancy factor of 1.0 with an average temperature factor for all atoms of 34 Å 2 . An RMSD of 0.27 for all CA's of the tetramer is observed when the crosslinked deoxyhemoglobin is compared with deoxyhemoglobin refined by using a similar protocol, 2HHD [Fronticelli et al. J. Biol. Chem. 269: 23965-23969, 1994]. Thus, no significant perturbations in the tertiary or quaternary structure are introduced by the presence of the sebacyl residue. However, the sebacyl residue does displace seven water molecules in the  cleft and the conformations of the  1 Lys82 and  2 Lys82 are altered because of the crosslinking. The carbonyl oxygen that is part of the amide bond formed with the NZ of  2 Lys82 forms a hydrogen bond with side chain of  2 Asn139 that is in turn hydrogen-bonded to the side chain of  2 Arg104. A comparison of the observed conformation with that modeled [Bucci et al. Biochemistry 35:3418-3425, 1996] shows significant differences. The differences in the structures can be rationalized in terms of compensating changes in the estimated freeenergy balance, based on differences in exposed surface areas and the observed shift in the side-chain hydrogen-bonding pattern involving  2 Arg104,  2 Asn139, and the associated sebacyl carbonyl group. Proteins 30:309-320, 1998.