The organ that surrounds the urethra and secretes an antibiotic protein is the

The Prostate gland

The prostate is a walnut-sized organ that surrounds the first part of the urethra. It is located between the bladder and the penis. Semen is formed by the prostate by combining a thick white fluid it initially produced with the sperm from the testicles. It also produces an antibiotic protein known as prostate-specific antigen (PSA) that changes the semen into liquid.