Nelfinavir is an inhibitor of HIV-1 protease, and is used for treatment of patients suffering from HIV/AIDS. However, treatment results in drug resistant mutations in HIV-1, protease. N88D and N88S are two such mutations which Occur in the non-active site region of the enzyme. We have determined crystal structures of unliganded N88D and N88S mutants of HIV-1 protease to resolution of 1.65 angstrom and 1.8 angstrom, respectively. These structures refined against synchrotron data lead to R-factors of 0.1859 and 0.1780, respectively. While structural effects of N88D are very subtle, the mutation N88S has caused a significant conformational change in D30, an active site residue crucial for substrate and inhibitor binding. (C) 2009 Elsevier Inc. All rights reserved.