The advent of HIV protease inhibitor (PI) therapy was a major advance in the treatment of HIV infection. Combined treatment of HIV-infected patients with reverse transcriptase inhibitors and PIs (intensive antiretroviral therapy, IART) has been shown to delay the onset of overt disease and to prolong survival. Current guidelines recommend the use of IART for the treatment of all newly diagnosed cases of HIV infection. Unfortunately, IART is associated with the development of numerous metabolic abnormalities, including peripheral lypodystrophy, hyperlipemia, insulin resistance, glucose intolerance, and type 2 diabetes. The reported incidence of type 2 diabetes in PI-treated patients is at least 10- fold greater than that in the general age- and sex-matched population and is particularly alarming considering the relatively young age of the patient populations and the rapidity of diabetes onset after the start of therapy. PIs have recently been shown to rapidly and selectively suppress the activity of Glut4, the insulin-responsive glucose transporter, an effect that can directly account for the insulin resistance and increased incidence of diabetes associated with PI therapy. The long-term goal of this proposal is to elucidate the relationship between the effect of PIs on Glut4 and the metabolic abnormalities associated with IART and to determine the mechanism of the effect of PIs on Glut4 activity. To accomplish these goals, the following specific aims will be pursued: 1) To determine the acute effect of PIs on whole body glucose disposal and glucose transport in skeletal muscle. This aim will directly test the hypothesis that Pls acutely induce whole-body insulin resistance via the inhibition of skeletal muscle Glut4. 2) To determine whether PIs suppress insulin-stimulated glucose transport by direct binding to Glut4. This aim will ascertain whether the PI effect is due to competitive or noncompetitive binding to Glut4 or binding to a molecule involved in the regulation of Glut4 activity in the plasma membrane. 3) To determine whether PIs suppress the activity of Glut isoforms other than Glut4. This aim will address a potentially important clinical issue: whether PIs, as a result of the inhibition of one or more of the other 8 known Glut isoforms, may have iatrogenic effects that have not yet been detected. 4) To determine the structural determinants of Glut4 interaction with PIs. This aim will identify specific Glut4 domains and amino acid residues involved in its predicted binding to PIs.