Conformational changes of the insulin receptor upon insulin binding and activation as monitored by fluorescence spectroscopy

We have characterized the changes in intrinsic fluorescence that the insulin receptor undergoes upon ligand binding and autophosphorylation. The binding of insulin to its receptor results in an increase in the receptor's fluorescence intensity, emission energy and anisotropy. We monitored the time course of the anisotropy change, and these data, coupled with studies monitoring the energy transfer from insulin receptor tryptophan donors to a fluorescent-labeled insulin, allowed us to conclude that the change in anisotropy is due to a conformational change in the receptor induced by hormone binding. Since insulin association is very fast, the time course also allowed us to estimate the slower rate of formation of this conformationally-altered state. The time course of receptor autophosphorylation was measured under similar conditions and was found to be similar to the ligand-induced anisotropy time course. The simultaneous use of two fluorescent-labeled insulin analogs also allowed us to assess the maximum distance between the two hormones bound to the receptor. Addition of ATP produces a large, seemingly instantaneous increase in anisotropy. Our observation that ATP binds to the insulin receptor in the presence and absence of insulin supports the idea that the conformational change produced by insulin binding increases the rate of autophosphorylation rather than increases ATP affinity. A suggested model for these changes is presented.     

Anterior temporal abnormality in temporal lobe epilepsy: a quantitative MRI and histopathologic study

OBJECTIVE: To examine the nature and frequency of anterior temporal lobe (AT) abnormalities that occur in intractable temporal lobe epilepsy (TLE). METHODS: We reviewed the MR scans and clinical histories of 50 consecutive patients with intractable TLE. Histopathology was available in 42 surgically treated cases. RESULTS: MRI demonstrated loss of the gray-white matter differentiation and decreased T1- and increased T2-weighted signal in the ipsilateral AT in 58% of the 50 patients. This appearance was observed in 64% of the 36 patients with hippocampal sclerosis (HS) but was also seen in patients without HS. These changes were associated with temporal lobe atrophy, a higher hippocampal T2 relaxation time, and a history of febrile convulsions. Pathologic examination showed that the MRI appearances were not caused by dysplasia, degenerative abnormalities, or inflammatory change. Histologic quantitation showed increased glial cell nuclei counts in the intractable TLE cases compared with controls. There was no difference in glial cell numbers between cases with AT abnormality and those without this appearance. Presence or absence of changes was not predictive of preoperative neuropsychology, postoperative change in neuropsychology, or seizure outcome after surgery. CONCLUSIONS: These frequently seen ipsilateral changes are not caused by gliosis and may reflect a nonspecific increase in water content in the temporal lobe. This may be due to myelin abnormalities or some other as yet unidentified pathologic factor.