Thiamine Diphosphate-Dependent Biocatalysis in the 21^st Century

Over the past three decades, the field of research on thiamine diphosphate (ThDP)-dependent enzymes has expanded remarkably, revealing a broad catalytic repertoire and versatility in synthetic applications. In parallel, considerable progress has been made in elucidating the reaction mechanisms. In this account, we discuss the fundamental features of ThDP-dependent enzyme catalysis, focusing on developments reported since the beginning of this century, with an emphasis on studies from recent years. We provide an overview of advances in C─C forming reactions, the relationships of sequence, structure, and function, as well as enzyme classifications and biocatalytic applications that have broadened ThDP-dependent research. In addition, we highlight newly described activities, including C₁ elongation and photobiocatalytic transformations, that have recently expanded the known catalytic scope of ThDP-dependent enzymes and paved the way to previously unexpected directions. Focusing on non-canonical enzymes and less established properties of ThDP-dependent enzymes, we also outline some of the remaining open questions and, at the same time, exciting new avenues for future research. The review aims to offer concise and critical insights into the current state of knowledge regarding ThDP-dependent enzymes. By selecting recent key developments and remaining challenges, we hope to stimulate further discoveries through an open-minded approach.