Abstract
Pyrroloquinoline quinone (PQQ) is an important cofactor of calcium- and lanthanide-dependent alcohol dehydrogenases, and has been known for over 30 years. Crystal structures of Ca-MDH enzymes (MDH is methanol dehydrogenase) have been known for some time; however, crystal structures of PQQ with biorelevant metal ions have been lacking in the literature for decades. We report here the first crystal structure analysis of a Ca-PQQ complex outside the protein environment, namely, poly[[undecaaquabis(μ-4,5-dioxo-4,5-dihydro-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylato)tricalcium(II)] dihydrate], {[Ca3(C14H3N2O8)2(H2O)11]·2H2O}n. The complex crystallized as Ca3PQQ2·13H2O with Ca2+ in three different positions and PQQ3-, including an extensive hydrogen-bond network. Similarities and differences to the recently reported structure with biorelevant europium (Eu2PQQ2) are discussed.
Highlights
Pyrroloquinoline quinone (PQQ) is the redox cofactor of glucose dehydrogenase enzymes and alcohol dehydrogenases
PQQ–metal complexes were reported with the trivalent lanthanides La3+, Eu3+ and Lu3+, and with Ca2+ (Lumpe & Daumann, 2019)
While no further structural information could be provided in that study, we were recently able to verify the proposed stoichiometry by the crystal structure of an Eu– PQQ complex with the net formula Eu2PQQ2Á12H2O (Lumpe et al, 2020)
Summary
Pyrroloquinoline quinone (PQQ) is the redox cofactor of glucose dehydrogenase enzymes and alcohol dehydrogenases. The first crystal structure of a europium–PQQ complex outside the MDH network was published through a collaborative effort and was reported as an Eu2PQQ2 structure (Lumpe et al, 2020) (Fig. 2). In light of those advances and the still scarce structural information available about PQQ–metal interactions, we present here the first crystal structure of a Ca– PQQ complex without the need of structural PQQ analogs or additional co-ligands.
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