The folding of a family of three-helix bundle proteins: spectrin R15 has a robust folding nucleus, unlike its homologous neighbours

Three homologous spectrin domains have remarkably different folding characteristics. We have previously shown that the slow-folding R16 and R17 spectrin domains can be altered to resemble the fast folding R15, in terms of speed of folding (and unfolding), landscape roughness and folding mechanism, simply by substituting five residues in the core. Here we show that, by contrast, R15 cannot be engineered to resemble R16 and R17. It is possible to engineer a slow-folding version of R15, but our analysis shows that this protein neither has a rougher energy landscape nor does change its folding mechanism. Quite remarkably, R15 appears to be a rare example of a protein with a folding nucleus that does not change in position or in size when its folding nucleus is disrupted. Thus, while two members of this protein family are remarkably plastic, the third has apparently a restricted folding landscape.

The occurrence of tooth size discrepancies among different malocclusion groups

This study consisted of 109 patients with varying malocclusions (Class I; Class II, Division 1; Division 2; and Class II surgery) who were treated orthodontically. Tooth size analyses were performed on the pretreatment models of these patients and mesial-distal tooth size ratios were measured as described by Bolton. The incidence of mesial-distal tooth size discrepancies in the malocclusion groups was analyzed and compared with Bolton's means and standard deviations. The results showed no difference in the incidence of tooth size discrepancies from one malocclusion group to another. When the sample was taken as a whole, there was no significant difference in the mean of the mesial-distal tooth size ratios as computed in the present study and compared to Bolton's mean. There were, however, higher standard deviations seen in the present study compared with Bolton's study. Even though there was no significant difference in the incidence of tooth size discrepancies among malocclusion groups, there was a large number of tooth size discrepancies in each group. Therefore it is suggested that Bolton's tooth size analysis be performed before initiation of orthodontic treatment.