Chemical Synthesis of Secretoglobin 3A2 Covalent Homodimer and Photocaged Monomeric Variants.

Secretoglobin (SCGB) 3A2 belongs to an intriguing family of small, secreted proteins present only in mammals. Although members of the SCGB protein family have distinct amino-acid sequences, they share structural similarities. Of particularly interest is the not yet fully understood self-assembly ability of SCGBs, which arise from covalent disulfide dimerization and non-covalent oligomerization. Recently, SCGB3A2 has attracted attention for its singular expression profile in airways. However, the knowledge on SCGB3A2 (patho)physiology derives exclusively from in-vivo and complex ex-vivo mixtures, which hampers characterization of the mechanisms driving SCGB3A2 structural behavior. In this report, we document the chemical synthesis of SCGB3A2 in multi-milligram quantities. Key to access both monomeric and homo-dimeric SCGB3A2 analogues was the use of KAHA ligation and enabled masking of the cysteine residue. The synthetic proteins were used to investigate SCGB3A2 self-assembly profile, confirming their high propensity to dimerization even in the absence of the key Cys residue.