Abstract：
:The influence of the amino acid residues surrounding the flavin ring in the flavodoxin of the cyanobacterium Anabaena PCC 7119 on the electron spin density distribution of the flavin semiquinone was examined in mutants of the key residues Trp(57) and Tyr(94) at the FMN binding site. Neutral semiquinone radicals of the proteins were obtained by photoreduction and examined by electron-nuclear double resonance (ENDOR) and hyperfine sublevel correlation (HYSCORE) spectroscopies. Significant differences in electron density distribution were observed in the flavodoxin mutants Trp(57) --> Ala and Tyr(94) --> Ala. The results indicate that the presence of a bulky residue (either aromatic or aliphatic) at position 57, as compared with an alanine, decreases the electron spin density in the nuclei of the benzene flavin ring, whereas an aromatic residue at position 94 increases the electron spin density at positions N(5) and C(6) of the flavin ring. The influence of the FMN ribityl and phosphate on the flavin semiquinone was determined by reconstituting apoflavodoxin samples with riboflavin and with lumiflavin. The coupling parameters of the different nuclei of the isoalloxazine group, as detected by ENDOR and HYSCORE, were very similar to those of the native flavodoxin. This indicates that the protein conformation around the flavin ring and the electron density distribution in the semiquinone form are not influenced by the phosphate and the ribityl of FMN.
journal_name
Biophys Jjournal_title
Biophysical journalauthors
Medina M,Lostao A,Sancho J,Gómez-Moreno C,Cammack R,Alonso PJ,Martínez JIdoi
10.1016/S0006-3495(99)77017-7subject
Has Abstractpub_date
1999-09-01 00:00:00pages
1712-20issue
3eissn
0006-3495issn
1542-0086pii
S0006-3495(99)77017-7journal_volume
77pub_type
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