Homodimerization interface of the RBPMS RRM. (a) Electrostatic
surface representation of the dimeric RBPMS RRM-RNA complex in the same view as
shown in Fig. 1c,
highlighting an electrostatic interaction between the basic and acidic residues
along the dimer interface. (b) Gel-filtration elution volumes
of the full-length RBPMS and RBPMS RRM (amino acids 11–114) plotted on
the Superdex75 column calibration curve. (c) An electrostatic
surface view of the dimer interface of molecule A with molecule B shown in a
cyan ribbon and stick representation. Residues of molecule B involved in the
dimer interface are labeled. Lys36 and Arg38 basic side chains interact with an
acidic patch on the surface, and Glu39, Asp34 and Asp87 acidic side chains
interact with a basic patch on the surface. (d) Details of the
RBPMS homodimerization interface in the complex, highlighting interactions
between residues involved in interfacial contacts. Residues of RRM molecules A
and B are colored purple and cyan, respectively. The view is approximately the
same in panel (c). (g) ITC-binding curves of complex formation between the 17-nt
GCACUUUCAACUUCACU ETF1 RNA target and the wild
type RBPMS RRM (black squares), and the RBPMS RRM containing mutations of
dimerization interface residues K36E/R38E (red diamonds), R38Q (green triangles)
and R38A/E39A (cyan triangles). Solid lines represent nonlinear least-squares
fit to the titration curve, with ΔH (binding enthalpy, kcal
mol−1), Ka (association
constant), and N (number of binding sites per monomer) as variable parameters.
Calculated values for Kd (dissociation constant) are
indicated.