The K homology module, one of the most common RNA-binding motifs, is present in multiple copies in both prokaryotic and eukaryotic regulatory proteins. Increasing evidence suggests that self-aggregation of KH modules has a functional role. We have used a combination of techniques to characterize the behavior in solution of the third KH domain of Nova-1, a paradigmatic KH protein. The possibility of working on the isolated module allowed us to observe specifically the homodimerization and RNA-binding properties of KH domains. We provide conclusive evidence that self-association of Nova-1 KH3 occurs in solution even in the absence of RNA. Homodimerization involves a specific protein/protein interface. We also studied the dynamical behavior of Nova-1 KH3 in isolation and in complex with RNA. These data provide a model for the mechanism of KH/RNA recognition and suggest functional implications of dimerization in KH complexes. We discuss our findings in the context of the whole KH family and suggest a generalized mode of interaction.

The human trefoil proteins TFF1 and TFF3 are expressed predominantly in the gastrointestinal tract. They are also expressed and regulated by estrogens in malignant breast epithelial cells. TFF1 and TFF3 are small cysteine-rich acidic secreted proteins of 60 and 59 amino acids with similar isoelectric points of 4.75 and 3.94, respectively. Each contains one trefoil domain that is characterized by several conserved features including six cysteine residues with conserved spacing. TFF1 and TFF3 form intermolecular disulfide bonds via an extra-trefoil domain cysteine residue and are present in vivo as monomers and homodimers and as complexes with other proteins. The TFF1 dimer is more active than the TFF1 monomer. In the present study the hydrodynamic and charge properties of TFF1 and TFF3 monomers and homodimers have been compared and shown to differ markedly. Notably, TFF1 is significantly more asymmetric than TFF3 (frictional coefficients 1.25 and 1.12, respectively, p < 0.001), and homodimerization of TFF1 results in a greater increase in asymmetry than for TFF3. The overall charges of TFF1 and TFF3 are very different at neutral pH. Titration curves predicted significant differences in charge across a wide pH range that agreed well with experimental data. The locations of charged amino acids in the primary sequences and in the tertiary structures of TFF1 and TFF3 were examined. This revealed interesting divergence in both the distribution and local topology of charged amino acid side chains. The significant differences between the shape, size, and surface charge of these two closely related molecules may account for their divergent biological activities.

The LLSAQ scoring system appeared to be a simple and effective technique to aid the diagnosis of adolescents who have AMS, and it may help improve the safety of large groups traveling to altitude. The AMS subjects tended to have low oxygen saturations and high pulse rates, highlighting potential areas for further research.