Major sperm protein

The Major Sperm Protein, commonly abbrieviated to MSP, is the most abundant protein in nematode sperm, making up about 15% of the total protein in the sperm cell. It is responsible for the cell's motility.

The MSP molecules are part of the cell cytoskeleton. They are built up into a set of long chains organised into bundles at the front of the cell, and are disassembled at the back. This pushes the cell forward in a process called treadmilling.

Although there are similar amino acid sequences in other organisms, MSP appears to be unique to the sperm of nematodes.