Protein modeling of cathepsin C mutations found in Papillon–Lefèvre syndrome

• Exon sequencing of cathepsin C gene was done in 6 Papillon–Lefèvre syndrome patients.
• One new and five known mutations with 2 types of polymorphisms were discovered.
• Protein modeling was performed for the P.35del L and the R272P mutations.
• Energy minimization has been performed to an acceptable degree.
• The models were analyzed in terms of stereochemical and geometrical parameters.

BackgroundPapillon–Lefèvre syndrome (PLS) is a rare autosomal recessive disorder characterized by hyperkeratosis involving the palms, soles, elbows, and knees followed by periodontitis, destruction of alveolar bone, and loss of primary and permanent teeth. Mutations of the lysosomal protease cathepsin C gene (CTSC) have been shown to be the genetic cause of PLS. This study analyzed CTSC mutations in five Iranian families with PLS and modeled the protein for mutations found in two of them.MethodsDNA analysis was performed by direct automated sequencing of genomic DNA amplified from exonic regions and associated splice intron site junctions of CTSC. RFLP analyses were performed to investigate the presence of previously unidentified mutation(s) in control groups. Protein homology modeling of the deduced novel mutations (P35 delL and R272P) was performed using the online Swiss-Prot server for automated modeling and analyzed and tested with special bioinformatics tools to better understand the structural effects caused by mutations in cathepsin C protein (CTSC).ResultsSix Iranian patients with PLS experienced premature tooth loss and palm plantar hyperkeratosis. Sequence analysis of CTSC revealed a novel mutation (P35delL) in exon 1 of Patient 1, and four previously reported mutations; R210X in Patient 2, R272P in Patient 3, Q312R in two siblings of family 4 (Patients 4 and 5), and CS043636 in Patient 6. RFLP analyses revealed different restriction fragment patterns between 50 healthy controls and patients for the P35delL mutation. Modeling of the mutations found in CTSC, P35delL in Patient 1 and R272P in Patient 3 revealed structural effects, which caused the functional abnormalities of the mutated proteins.ConclusionsThe presence of this mutation in these patients provides evidence for founder CTSC mutations in PLS. This newly identified P35delL mutation leads to the loss of a leucine residue in the protein. The result of this study indicates that the phenotypes observed in these two patients are likely due to CTSC mutations. Also, structural analyses of the altered proteins identified changes in energy and stereochemistry that likely alter protein function.