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Molecular mechanisms of ciprofloxacin-loaded nanoplastics on human serum albumin: Protein denaturation and binding site recognition
Summary
Scientists found that when tiny plastic particles (nanoplastics) team up with the antibiotic ciprofloxacin, the combo does more damage to a key blood protein called human serum albumin than either substance does alone, warping its shape and blocking its normal function. This matters because albumin helps carry nutrients, drugs, and hormones through your bloodstream, so this lab study suggests that pollution "cocktails" of plastics and antibiotics in the environment could pose a compounded health risk that we haven't been accounting for.
Nanoplastics (NPs) and antibiotics are prevalent environmental pollutants that coexist and interact in the environment, leading to complex multi-level toxicities. However, there is currently insufficient research on the effects of co-exposure to polystyrene nanoplastics (PSNPs) and ciprofloxacin (CIP) on key human proteins, such as human serum albumin (HSA), and the interaction mechanisms and binding modes between them remain unclear. This study investigated the effects of CIP-loaded PSNPs (PSNPs@CIP) on HSA's function and structure and explored the binding mode through site competition and molecular docking. The results revealed that PSNPs@CIP inhibited HSA's esterase-like activity (62.0 %), more significantly than CIP (72.2 %) or PSNPs (87.0 %), indicating stronger functional disruption. Meanwhile, PSNPs@CIP caused more severe structural disruption of HSA, including alterations in backbone conformation, secondary structure, and the amino acid microenvironment. PSNPs@CIP interfered with the n→π* electronic transition of the peptide backbone (absorption reduced by 0.99, red shift 6.0 nm), and promoted the decrease of α-helix content to 47.3 %. A red shift of 9.8 nm (Δλ=60 nm) indicated an altered tryptophan (Trp) microenvironment. CIP preferentially binds to Sudlow site I of HSA via hydrogen bonding with Ala215, Lys199, and Lys195. This study demonstrates that PSNPs@CIP composite contamination aggravates HSA structural and functional impairment by promoting the direct binding of CIP to Sudlow site I and facilitating HSA adsorption onto PSNPs as a "protein corona". This study elucidates the molecular-level mechanisms and binding modes of PSNPs@CIP affecting HSA, providing crucial evidence for assessing NPs co-pollution and environmental behavior.