Novel antilithiatic cationic proteins from human calcium oxalate renal stone matrix identified by MALDI-TOF-MS endowed with cytoprotective potential: An insight into the molecular mechanism of urolithiasis

Background: No substantial work has been conducted to date in context to cationic proteins with antilithiatic activity. We explored the antilithiatic cationic proteins present in human calcium oxalate (CaOx) stones and also examined their molecular interactions with calcium oxalate crystals in silico. Methods: Proteins were isolated from the matrix of human CaOx containing kidney stones. Proteins having MW>3 kDa were subjected to cation exchange chromatography followed by molecular-sieve chromatography. The effect of these purified cationic proteins was tested against CaOx nucleation and growth and on oxalate injured MDCK cells for their activity. Proteins were identified by MALDI-TOF MS. Molecular interaction studies with COM crystals in silico were also investigated. Results: Three antilithiatic cationic proteins were identified as histone-lysine N-methyltransferase, inward rectifier K channel and protein Wnt-2 (MW similar to 53, similar to 44, and similar to 42 kDa respectively) by MALDI-TOF MS based on database search with MASCOT server. Further molecular modeling calculations revealed the mode of interaction of these proteins with CaOx at the molecular level. Conclusion: We identified histone-lysine N-methyltransferase, inward rectifier K channel and protein Wnt-2 as novel antilithiatic proteins which play a vital role in the kidney function and have been associated with various kidney diseases. (c) 2012 Elsevier B.V. All rights reserved.