Mass Spectrometry Studies of 60 kDa Proteins Extracted from Calcium Oxalate Stones

We extracted proteins with a molecular weight of 60 kDa from human renal calcium oxalate stones. One-dimensional electrophoresis (SDS-polyacrylamide gel electrophoresis) with Coomassie blue stain was used for molecules separation. After in-gel digestion by trypsin, protein samples were analyzed using Nanospray liquid chromatography coupled to a quadrupole time-of-flight mass spectrometer. Peptide sequence analysis was performed by MASCOT Web searching and National Center for Biotechnology Information database comparison. Our results revealed that the matrix possess only 2.5% of stones in weights. Three most abundant 60 kDa proteins named myeloperoxidase, lactoferrin, and albumin were identified. Because albumin has been previously studied by many researchers including our team, we are highly interested to study the remaining two proteins. Later, their in vitro activities of crystallization were studied by employing methods such as nucleation, crystal growth, and aggregation. The mass spectra pattern of myeloper-oxidase and lactotransferrin precursor (lactoferrin) revealed modifications and deamidations, and their calcium oxalate stones crystallization studies revealed no effects on the nucleation, crystal growth, and aggregation. The mass spectra pattern of albumin indicated no amino acid modifications. In conclusion, we found three commonly seen 60 kDa proteins (albumin, myeloperoxidase and lactoferrin) in calcium oxalate stones in this study. Albumin has been tested before and has effect on stone formation. However, purchased myeloperoxidase and lactoferrin have no effect in the crystallization process; their role play in the process of stone formation should be further elucidated.