Metabolosomes

Metabolosomes are a class of bacterial microcompartments that enclose enzymes of specific metabolic pathways within a protein shell. They are a subset of bacterial microcompartments (BMCs) that sequester reactive intermediates, such as aldehydes, produced during metabolism, thereby improving reaction efficiency and protecting the cytoplasm.

These organelles consist of a selectively permeable protein shell assembled from BMC-domain shell proteins, which form hexameric, trimeric, and pentameric units. The interior houses one or more multienzyme cargo complexes, typically directed into the lumen by short encapsulation peptides appended to the cargo enzymes. The shell permits passage of small molecules while restricting toxic intermediates.

Metabolosomes have been most studied in the propanediol utilization (Pdu) and ethanolamine utilization (Eut) systems, found in bacteria such as Salmonella enterica and Escherichia coli. These systems encode operons that include both the cargo enzymes—for example, diol dehydratase in Pdu and ethanolamine ammonia-lyase in Eut—and the shell proteins. In many cases, B12-dependent reactions are involved in the interior chemistry.

Functionally, metabolosomes optimize the catabolism of substrates that generate reactive intermediates and may concentrate cofactors and enzymes to enhance turnover. They also reduce cytotoxicity by confining aldehydes and other reactive species within the shell.

Research into metabolosomes covers their biosynthesis, structural diversity, and evolution, as well as potential biotechnological applications in nanobiotechnology and metabolic engineering.