Mr. Starich et al., NMR STRUCTURE OF HMFB FROM THE HYPERTHERMOPHILE, METHANOTHERMUS-FERVIDUS, CONFIRMS THAT THIS ARCHAEAL PROTEIN IS A HISTONE, Journal of Molecular Biology, 255(1), 1996, pp. 187-203
The three-dimensional structure of the recombinant histone rHMfB from
Methanothermus fervidus, an archaeon that grows optimally at 83 degree
s C, has been determined by nuclear magnetic resonance methods. This i
s only the third structure of a protein from a hyperthermophilic organ
ism (optimal growth at temperatures above 80 degrees C). Signal assign
ments were made using a combination of homonuclear-correlated, N-15-do
uble resonance and N-15, C-13 triple resonance NMR experiments. Long r
ange dipolar interactions for the symmetric homodimer were identified
from two-dimensional C-13-double half-filtered and three-dimensional C
-13-filtered NMR data obtained for a heterolabeled-dimer. A family of
33 structures was calculated using DSPACE(TM) with a total of 609 NOE-
derived interproton distance restraints, including 22 intraresidue, 19
2 sequential, 300 medium-range (two to five residues), 86 long-range i
ntramolecular (more than five residues) and 112 intermolecular distanc
e restraints. The monomer subunits consist of three alpha-helices, ext
ending from residues Pro4 to Ala15 (helix I), Ser21 to Ala50 (helix II
) and Lys56 to Lys68 (helix III), as well as two short segments of bet
a-strand comprised of residues Arg19 to Ser21 and Thr54 to Ile55. Heli
ces I, II and III contain N-terminal capping boxes, and helices I and
II contain C-terminal caps. The structure of the (rHMfB)(2) dimer appe
ars very similar to the dimer subunits within the histone core octamer
of the chicken nucleosome. The presence of a canonical ''histone fold
'' motif in rHMfB is consistent with the HMf family of archaeal histon
es and the eukaryal nucleosome core histones having evolved from a com
mon ancestor. The (rHMf8)2 dimer contains several structural features
that may impart thermal stability (or non-lability), including two nov
el hydrophobic ''proline Ncaps'', four interhelical hydrogen bonds and
short N- and C-terminal disordered tails. (C) 1996 Academic Press Lim
ited