Xl. Huang et al., Formation of the single-layer beta-sheet of Borrelia burgdorferi OspA in the absence of the C-terminal capping globular domain, J MOL BIOL, 308(2), 2001, pp. 367-375
Borrelia outer surface protein A (OspA) contains a unique single-layer P-sh
eet that connects N and C-terminal globular domains. This singlelayer beta
-sheet segment (beta -strands 8-10) is highly stable in solution, although
it is exposed to Me solvent on both faces of the sheet and thus it does not
contain a hydrophobic core. Here, we tested whether interactions with the
C-terminal domain are essential for the formation of the single-layer P-she
et. We characterized the solution structure, dynamics and stability of an O
spA fragment corresponding to P-strands 1-12 (termed OspA[27-163]), which l
acks a majority of the C-terminal globular domain. Analyses of NMR chemical
shifts and backbone nuclear Overhauser effect (NOE) connectivities showed
that OspA[27-163] is folded except the 12th and final beta -strand. H-1-N-1
5 heteronuclear NOE measurements and amide H-H-2 exchange revealed that the
single-layer beta -sheet in this fragment is more flexible than the corres
ponding region in full-length OspA. Thermal-denaturation experiments using
differential scanning calorimetry and NMR spectroscopy revealed that the N-
terminal globular domain in the fragment has a conformational stability sim
ilar to that of the same region in the full-length protein, and that the si
ngle-layer beta -sheet region also has a modest thermal stability. These re
sults demonstrate that the unique single-layer beta -sheet retains its conf
ormation in the absence of its interactions with the C-terminal domain. Thi
s fragment is significantly smaller than the full-length OspA, and thus it
is expected to facilitate studies of the folding mechanism of this unusual
beta -sheet structure. (C) 2001 Academic Press.