How a mixture of urinary human serum albumin fragments survives in urine-mimicking pH conditions: Simulation studies

One of effective indicators for screening and tracking kidney and diabetic disorders is the microalbuminuria level. The fresh urine is required for effectively measuring a microalbuminuria level. The presence of urinary proteases leads to the albumin fragmentation which can interfere the results. Some albumin fragments are reported to be potential clinical biomarkers where their chemistry in urine is incompletely understood. This information is crucial for the effective detection of urinary albumin fragments. Recently, nine fragmented albumins (F1-F9) were identified in urine where no structural and dynamic information is available. Thus, in this work, the structural and dynamic properties of the F1-F9 aqueous mixture at urine pHs (pH 4.5, 7, and 8) are studied. Molecular Dynamics (MD) simulations are performed to understand the behaviour of fragmented albumin mixture in a molecular level. The spontaneous fragment aggregation is captured at all pHs where the complete aggregation is only found at pH 7 and 8. No specific aggregation mechanism is identified. The formation of fragment aggregate is driven by electrostatic interactions. Most fragments are unfolded. F8 is found to be the most stable fragment. F8 and other fragments are suggested to be potential disease biomarkers. The fragment aggregation found here can thus reduce the detection efficacy of urinary albumin fragments in a sample. The knowledge obtained here will be useful for urinary albumin detection, sample stability, and proteomic analysis of urine.