**Geldanamycin**  

**Definition:**  

Geldanamycin is a naturally occurring benzoquinone ansamycin antibiotic derived from *Streptomyces hygroscopicus*. It is known for its ability to inhibit heat shock protein 90 (Hsp90), a molecular chaperone critical for protein folding and stability.  

**Function:**  

Geldanamycin binds to Hsp90, disrupting its function and leading to the degradation of client proteins involved in cell growth, survival, and proliferation. This mechanism makes it a potent agent for targeting cancer cells and other diseases driven by abnormal protein activity.  

**Applications:**  

Geldanamycin is primarily used in research to study Hsp90 inhibition and its effects on cancer, neurodegenerative diseases, and viral infections. It also serves as a precursor for developing synthetic Hsp90 inhibitors with therapeutic potential.