Correlation between plasma homocyst(e)ine and aortic atherosclerosis
Plasma homocyst(e)ine [H(e)] levels correlate with the prevalence of arterial occlusive diseases. Recently, transesophageal echocardiography (TEE) has been used to evaluate patients with atherosclerotic plaques in the thoracic aorta. The purpose of this study was to determine whether H(e) levels correlate with the degree of atherosclerotic plaque in the thoracic aorta (ATH) as seen on TEE. Maximum plaque areas for three locations in the thoracic aorta (arch, proximal descending, and distal descending) were measured with TEE in 156 patients. Maximum plaque areas for these locations were added to yield an estimate of ATH. ATH and H(e) levels, and levels of folic acid, vitamin B12, and pyridoxal 5'-phosphate were measured in a double-blind manner. Univariate analysis demonstrated a significant correlation of H(e) with ATH (r = 0.3, p< 0.001). On multivariate analysis, H(e) was independently predictive of ATH (r for the model including H(e) was 0.63, p < 0.0001). Plasma H(e) levels are therefore significantly and independently correlated with the degree of atherosclerosis in the thoracic aorta
A single amino acid in the SH3 domain of Hck determines its high affinity and specificity in binding to HIV-1 Nef protein
We have examined the differential binding of Hck and Fyn to HIV-1 Nef to elucidate the structural basis of SH3 binding affinity and specificity. Full-length Nef bound to Hck SH3 with the highest affinity reported for an SH3-mediated interaction (KD 250 nM). In contrast to Hck, affinity of the highly homologous Fyn SH3 for Nef was too weak (KD > 20 microM) to be accurately determined. We show that this distinct specificity lies in a variable loop, the 'RT loop', positioned close to conserved SH3 residues implicated in the binding of proline-rich (PxxP) motifs. A mutant Fyn SH3 with a single amino acid substitution (R96I) in its RT loop had an affinity (KD 380 nM) for Nef comparable with that of Hck SH3. Based on additional mutagenesis studies we propose that the selective recognition of Nef by Hck SH3 is determined by hydrophobic interactions involving an isoleucine residue in its RT loop. Although Nef contains a PxxP motif which is necessary for the interaction with Hck SH3, high affinity binding was only observed for intact Nef protein. The binding of a peptide containing the Nef PxxP motif showed > 300-fold weaker affinity for Hck SH3 than full-length Nef.