Variety of size and form of GRM2 bacterial microcompartment particles

Abstract

Bacterial microcompartments (BMCs) are bacterial organelles involved in enzymatic processes, such as carbon fixation, choline, ethanolamine and propanediol degradation, and others. Formed of a semi-permeable protein shell and an enzymatic core, they can enhance enzyme performance and protect the cell from harmful intermediates. With the ability to encapsulate non-native enzymes, BMCs show high potential for applied use. For this goal, a detailed look into shell form variability is significant to predict shell adaptability. Here we present four novel 3D cryo-EM maps of recombinant Klebsiella pneumoniae GRM2 BMC shell particles with the resolution in range of 9 to 22 Å and nine novel 2D classes corresponding to discrete BMC shell forms. These structures reveal icosahedral, elongated, oblate, multi-layered and polyhedral traits of BMCs, indicating considerable variation in size and form as well as adaptability during shell formation processes.

Keywords: GRM2; Klebsiella pneumoniae; bacterial microcompartments; cryo-EM.

FIGURE 1

Cryo‐EM classification and identification of BDPs. Text box in the top left of the left panel refers to previously described pT = 4 and pT = 4, Q = 6 BDP forms present in our sample but not analyzed closer in this study

FIGURE 2

Exemplary micrographs of larger asymmetric BDPs formed by the higher order polyhedral fusions (marked with an arrow)

FIGURE 3

Variability and relations of the BDP subspecies