Coagulation factor IXa: the relaxed conformation of Tyr99 blocks substrate binding.
Hopfner, K.P., Lang, A., Karcher, A., Sichler, K., Kopetzki, E., Brandstetter, H., Huber, R., Bode, W., Engh, R.A.(1999) Structure 7: 989-996
- PubMed: 10467148 
- DOI: 10.1016/s0969-2126(99)80125-7
- Primary Citation of Related Structures:  
1RFN - PubMed Abstract: 
Among the S1 family of serine proteinases, the blood coagulation factor IXa (fIXa) is uniquely inefficient against synthetic peptide substrates. Mutagenesis studies show that a loop of residues at the S2-S4 substrate-binding cleft (the 99-loop) contributes to the low efficiency ...