Biological and structural characterization of the Type 3 fimbrial subunit MrkA from Klebsiella pneumoniae

Klebsiella pneumoniae is a Gram‐negative opportunistic pathogen responsible for a wide range of community‐associated and hospital‐acquired infections and a major cause of neonatal sepsis in low‐ and middle‐income countries. The pathogen's surface fimbriae, particularly the Type 3 fimbriae, are critical for bacterial adhesion, biofilm formation, and host defense evasion. MrkA, the pathogen's major Type 3 fimbrial subunit, has a structural function in fimbrial assembly, but its three‐dimensional structure remains to be fully elucidated. In this study, we utilized solution‐state nuclear magnetic resonance spectroscopy to elucidate the structure of MrkA, leveraging previously reported chemical shift assignments of a designed self‐complementing monomeric protein. Additionally, we confirmed the ability of monoclonal antibodies, capable of recognizing MrkA oligomers on wild‐type Klebsiella bacteria, to bind the recombinant MrkA protein. Our findings contribute to the evaluation of MrkA as a potential target in vaccine development against Klebsiella pneumoniae infections.