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Title
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The three-dimensional NMR-solution structure of the polypeptide fragment 195-286 of the LFB1/HNF1 transcription factor from rat liver comprises a nonclassical homeodomain.
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Authors
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B.Leiting,
R.De Francesco,
L.Tomei,
R.Cortese,
G.Otting,
K.Wüthrich.
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Ref.
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Embo J, 1993,
12,
1797-1803.
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PubMed id
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Abstract
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The three-dimensional backbone fold of a polypeptide fragment from the rat
LFB1/HNF1 transcription factor was determined by nuclear magnetic resonance
(NMR) spectroscopy in solution. This fragment contains an amino acid sequence
that is approximately 22% homologous to the well known homeodomains, but which
contains 81 amino acid residues as compared with 60 residues in 'typical'
homeodomains. For the present studies we used a recombinant 99 amino acid
polypeptide containing this sequence in positions 10-90, which was uniformly
labelled with 15N and also doubly labelled with 15N and 13C. The NMR structure
of this polypeptide contains three alpha-helices comprising the residues 18-29,
36-50 and 71-84, a loop formed by residues 30-35, and a long stretch of
non-regular secondary structure linking the second and third helices. The
relative location and orientation of the helices is very similar to that in the
Antennapedia (Antp) homeodomain structure, despite the fact that helix II is
elongated by about one turn. This confirms a recently advanced hypothesis based
on sequence comparisons that this polypeptide segment of LFB1/HNF1 might
represent a homeodomain-like structural element. The helix-turn-helix motif,
which has been shown to comprise the DNA recognition helix in the Antp
homeodomain, can readily be recognized in the LFB1/HNF1 homeodomain, in spite of
an extensive modification of the primary structure. The two residues of the
tight turn in the Antp homeodomain are replaced by a 23 residue linker region
between the two helices in LFB1/HNF1, which bulges out from the rest of the
molecule and thus enables the formation of a non-classical helix--turn--helix
motif.
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