Adapter protein involved in neuronal nitric-oxide (NO) synthesis regulation via its association with nNOS/NOS1. The complex formed with NOS1 and synapsins is necessary for specific NO and synapsin functions at a presynaptic level. Mediates an indirect interaction between NOS1 and RASD1 leading to enhance the ability of NOS1 to activate RASD1. Competes with DLG4 for interaction with NOS1, possibly affecting NOS1 activity by regulating the interaction between NOS1 and DLG4 (By similarity). In kidney podocytes, plays a role in podosomes and filopodia formation through CDC42 activation (PubMed:33523862). Interacts with the PDZ domain of NOS1 or the second PDZ domain of DLG4 through its C-terminus. Interacts with RASD1 and SYN1, SYN2 and SYN3 via its PID domain. Forms a ternary complex with NOS1 and RASD1. Forms a ternary complex with NOS1 and SYN1. Expressed in kidney glomeruli podocytes. Genetic variation in NOS1AP influences the electrocardiographic QT interval [MIM:610141]. The QT interval is defined as the time from the beginning of the Q wave to the end of the T wave, representing the duration of ventricular electrical activity. The QT interval, a measure of cardiac repolarization, is a genetically influenced quantitative trait with considerable medical relevance: both high and low values are associated with increased risk of cardiovascular morbidity and mortality. The disease is caused by variants affecting the gene represented in this entry. Extended N-terminus.