(a) Multiple sequence alignment of hexameric QPRT homologs. The
database and accession code of aligned sequences are indicated in
parentheses. Homo sapiens QPRT, human (Uniprot code Q15274); Sus
scrofa QPRT, porcine (PDB code 4I9A); Bos taurus QPRT, bovine
(NCBI code AAI02551); Rattus norvegicus QPRT, rat (NCBI code
AAH88177); Saccharomyces cerevisiae QPRT, yeast (PDB code 3C2E);
Helicobacter pylori QPRT, Hp (PDB code 2B7N); Mycobacterium
tuberculosis QPRT, Mt (PDB code 1QPO); Thermus thermophilus
QPRT, Tt (PDB code 1 × 1O). Red box
indicates N-terminal helix α1. Annotation of helices
α1–α3 (blue cylinders) corresponding to
HsQPRT. Residue numbers are based on human protein. (b)
Location of helix α1. Six α1 helices in the
hexameric protein are shown as red ribbons. (c) Intermolecular
interaction between helix α1 and helix α3 of the
adjacent dimer (stereographic views). Residues of helix α3 in
the adjacent dimer (MolE) are primed. (d) Size exclusion
chromatographic analysis of HsQPRT in wild-type (blue),
NΔ4 (light blue), NΔ8 (green), NΔ9
(yellow), NΔ10 (orange) and NΔ12 (red). The sample
state was confirmed using SDS-PAGE. (e) Heat aggregation profile of
HsQPRT. Time intervals of approximately 2 min
(1 °C) are given between data points. Full-length
and NΔ9 mutant proteins are labelled as circles and triangles,
respectively.