Insulin Receptor Fragmentation by Matrix Metalloprotease 1

Insulin resistance is a hallmark of diabetes, a disease that costs healthcare systems hundreds of billions of dollars annually, and although the exact mechanism behind insulin resistance has not been identified, the reduced tyrosine activity of the integral membrane protein insulin receptor (IR) and its decreased cell surface presentation have been linked to insulin resistance. Moreover, IR shedding, the proteolytic cleavage of extracellular domains of IR releasing soluble fragments into blood, has been correlated with diabetes outcomes. We hypothesized that MMP1 may bind the IR and fragment it, thus inducing insulin resistance and contributing to comorbidities. After introducing MMP1 to the IR and using LC-MS, 21 fragments of the IR were identified. MMP1 and the IR, both active and inactive, were submitted to ClusPro and every ClusPro model was siphoned through to find the closest distance that the MMP1 catalytic site is to the cleavage sites of each fragment. The catalytic site distance varied from under 5 angstroms to more than 30 angstroms. The B-Factor across the IR was also calculated to determine the ability for each fragment to flex in a way that the catalytic site could reach it, but the B-Factors were unexpectedly low. A sequence logo was made for the cleavage sites of each fragment and compared to the MEROPS MMP1 cleavage site sequence logo with little overlap. Results such as distances from catalytic site to cleavage site being under 10 angstroms are suggestive of interaction between MMP1 and the IR, although other results such as there being little similarity between the sequence logos dispute that. This may be due to trace amounts of trypsin found within the LC-MS samples and future works would require validation through inhibiting trypsin within the samples.