BINDING-SITES FOR MG(II) IN H-ATPASE FROM BACILLUS PS3 AND IN THE ALPHA(3)BETA(3)GAMMA SUBCOMPLEX STUDIED BY ONE-DIMENSIONAL ESEEM AND 2-DIMENSIONAL HYSCORE SPECTROSCOPY OF OXOVANADIUM(IV) COMPLEXES - A POSSIBLE ROLE FOR BETA-HIS-324()

The binding sites for Mg2+ in wild type F1 ATPase (TF1) and in the alp ha(3) beta(3) gamma subcomplex from the thermophilic bacterium Bacillu s PS3 have been studied by EPR and by ESEEM and HYSCORE spectroscopy o f complexes with the oxovanadium cation VO2+. Complexes of metal-deple ted TF1 and substoichiometric amounts of VO2+ display low-temperature EPR signals with spectral parameters g(parallel to) = 1.947 and g(perp endicular to) = 1.980, and hyperfine couplings with V-51, A(parallel t o) = 169 x 10(-4) cm(-1) and A(perpendicular to) = 61 x 10(-4) cm(-1), that are indicative of a binding site for VO2+ with nitrogen ligands from the protein. This binding site is probably identical with the met al binding site with strong affinity MI that has been characterized us ing Mn2+ in a previous study [Buy, C., Girault, G., & Zimmermann, J. L . (1996) Biochemistry 35, 9880-9891]. The three-pulse ESEEM spectrum o f the VO2+ complex with TF1 shows a frequency pattern with spectral pr operties that are evidence for two nitrogen ligands to the VO2+ with h yperfine couplings A(1) = 4.75 MHz and A(2) = 6.5 MHz and nuclear quad rupole parameters e(2)Q(q1) = 2.8-3.2 MHz and e(2)Q(q2) = 2.0-2.3 MHz. The ligands are identified as a lysine terminal amine and a histidine imidazole, which are proposed as Lys-164 and His-324 from a beta subu nit. The HYSCORE data obtained for the VO . TF1 complex show correlati ons within each pair of the ESEEM nu(dq) peaks from the N-14 nuclei, c onfirming the interpretation of the one-dimensional spectra. Evidence for the formation of a ternary complex by addition of VO2+ and ATP to metal-depleted TF1 is shown in the EPR and ESEEM spectra and in the co ntour plots of the HYSCORE data. Two pairs of correlation patterns are resolved in addition to the peaks from the two N-14 ligands, which ar e interpreted as hyperfine couplings with P-31(beta) and P-31(gamma) O f the ATP that binds the VO2+ cation, The assignment of the two hyperf ine couplings to the specific phosphates, A(P-31(beta)) = 15.5 MHz and A(P-31(gamma)) = 8.7 MHz, in the VO . TF1 . ATP complex is proposed b y comparison with those measured for VO2+ in solution with ATP at pH 6 .3 and 2.3. These results are discussed in light of the previous data with the analogous Mn . TF1 complex, and a model is proposed in which the native Mg2+ in the M1 site is coordinated by the side chain of bet a-Lys-164 and is in close proximity to a histidine residue (probably b eta-His-324) that may have a critical role. Additional coordination by two phosphates from ATP (probably the beta- and gamma-phosphates) is observed in the ternary complex VO . TF1 . ATP. ESEEM and HYSCORE data are also obtained for the analogous complexes VO .alpha(3) beta(3) ga mma and VO .alpha(3) beta(3) gamma . ATP that show very similar proper ties in terms of coordination of the divalent metal cation, except for the lysine ligand that is found to be lost in the ternary complex wit h ATP. It is suggested that this observation may reflect changes in th e metal and nucleotide active sites that are associated with the absen ce of the delta and epsilon subunits in the subcomplex.