scruin

Actin-binding protein found associated with the acrosomal process of Limulus polyphemus sperm. Scruin holds the microfilaments of the core process in a strained configuration so that the process is coiled. The myosin binding sites on the microfilaments are blocked so HMM decoration is impossible, indicating that there is an unusual packing conformation; when the scruin-actin binding is released the process straightens, the conformation of the actin changes and myosin binding is possible.