 Its family generally bind to PXXP sites, but in MAGUKs it is known to bind to other sites as well.One of the most well known features is that it can form an intramolecular bond with the GUK domain, creating what is known as a GUK-SH3 'closed' state.The regulatory mechanisms and function are unknown but it is hypothesized that it may involve a hook region and a calmodulin binding region located elsewhere in the gene.