Gold Nanoparticles as a Possible Tool to Untangle Some Structural Features of the Gluten Network

Aqueous semolina suspensions were reacted with spherical gold nanoparticles (AuNPs, nominal diameter, 20 nm) to assess the accessibility of cysteine thiols in durum wheat proteins, focusing on network-forming gluten proteins. Unlike small thiol reagents, covalent bond formation between gold ions on the AuNPs surface and protein thiols was greatly facilitated by the addition of 1% sodium dodecyl sulfate (SDS). SDS weakens non-covalent hydrophobic interactions within and among proteins, increasing the exposure of buried thiols without altering disulfide bonds. MS/MS analysis of proteolytic fragments from the isolated AuNP-protein covalent complexes allowed identification of the bound proteins. Proteomics data suggests that AuNPs also associate with gluten proteins lacking free thiols in their native structure, which are bound to AuNPs by forming disulfide bonds with other gluten proteins containing accessible thiols, via thiol-disulfide exchange reactions. This implies that thiol-disulfide reshuffling among gluten proteins occurs already in the grain, enabling proteins without free thiols to become part of AuNP-bound assemblies and revealing specific protein species involved in these early interactions. These observations highlight the role of thiol-disulfide exchange within the grain matrix, elucidating how such molecular rearrangements influence the topology and strength of protein networks in food and in related biopolymeric systems. Results of this exploratory study are discussed for their molecular relevance and for the potential use of size-based analytical and structural approaches in other biological contexts.