HAX-1 Structural Studies and Interactions with the SERCA/Phospholamban Complex

HAX-1 has become a highly relevant protein over the past many years as it has been identified in several subcellular locations, is involved with apoptosis, and is implicated in many diseases including multiple types of cancer, congenital neutropenia, and heart disease. Structural studies will be essential to gaining insight into how HAX-1 interacts with other protein partners and plays a role in these multiple diseases.Heart muscle contractility is a completed process which is dictated by a diverse network of proteins. The sarco(endo)plasmic reticulum Ca2+ -ATPase, SERCA, is responsible for transporting calcium from the cytosol into the SR, promoting muscle relaxation. SERCA is regulated by phospholamban, a small 52 amino acid transmembrane protein. HAX-1 has been recently identified as a novel interaction partner with this complex. The SERCA/PLN complex has already been identified as being a highly regulated complex necessary for achieving proper regulation. Therefore, the complete molecular and biochemical understanding of the SERCA/PLN complex, along with interactions from other regulatory proteins, is necessary for the development of therapies.In this work, we use solution and solid-state NMR to study the structure of HAX-1 alone and the interactions with the complex. In addition, we have performed biochemical assays to determine the effects on SERCA activity. The SERCA/PLN is a high-profile drug target because of its involvement in many cardiovascular diseases. The complete structural characterization of HAX-1 and its interactions with the SERCA/PLN complex, as well as with other protein partners, will prove essential for understanding the role of HAX-1 in heart pathologies and other devastating diseases.