Biosynthesis of the modified tetrapyrroles—the pigments of life

Abstract

Modified tetrapyrroles are large macrocyclic compounds, consisting of diverse conjugation and metal chelation systems and imparting an array of colors to the biological structures that contain them. Tetrapyrroles represent some of the most complex small molecules synthesized by cells and are involved in many essential processes that are fundamental to life on Earth, including photosynthesis, respiration, and catalysis. These molecules are all derived from a common template through a series of enzyme-mediated transformations that alter the oxidation state of the macrocycle and also modify its size, its side-chain composition, and the nature of the centrally chelated metal ion. The different modified tetrapyrroles include chlorophylls, hemes, siroheme, corrins (including vitamin B12), coenzyme F430, heme d1, and bilins. After nearly a century of study, almost all of the more than 90 different enzymes that synthesize this family of compounds are now known, and expression of reconstructed operons in heterologous hosts has confirmed that most pathways are complete. Aside from the highly diverse nature of the chemical reactions catalyzed, an interesting aspect of comparative biochemistry is to see how different enzymes and even entire pathways have evolved to perform alternative chemical reactions to produce the same end products in the presence and absence of oxygen. Although there is still much to learn, our current understanding of tetrapyrrole biogenesis represents a remarkable biochemical milestone that is summarized in this review.

Opportunities and challenges for assigning cofactors in cryo-EM density maps of chlorophyll-containing proteins

“…Chls are a major subfamily of the larger class of biomolecules known as tetrapyrroles and there are approximately 15 major types of Chls and bacteriochlorophylls 27 . The structural differences among the four major types of Chls ( a , b , d , and f ) found in cyanobacteria and higher plants are subtle but are functionally important (Supplementary Fig.…”

“…Chl d also has a formyl group at position C3 where Chl a has a vinyl group. Finally, divinyl-Chl a and divinyl-Chl b are minor Chls similar to Chls a and b , but they have a vinyl group at C8 instead of an ethyl moiety 27 , which improves the blue-light-harvesting capabilities of some marine Prochlorococcus spp. by allowing them to harvest light not absorbed by Chl a .…”

In situ formation of photoactive B-ring reduced chlorophyll isomer in photosynthetic protein LH2

“…Cyclic tetrapyrroles with modified skeletons and peripheral groups have essential roles in various biofunctional proteins 1 – 3 . Chlorophyll (Chl) molecules, involved in the solar-energy conversion processes of oxygenic photosynthesis, typically contain an unsymmetrical conjugated tetrapyrrole π-system, in which the C17–C18 bond in the D-ring is hydrogenated 1 , 4 – 8 . The D-ring reduced chlorin (17,18-dihydroporphyrin) skeleton is responsible for efficient light absorption in the visible portion of the solar spectrum.…”

“…The D-ring reduced chlorin (17,18-dihydroporphyrin) skeleton is responsible for efficient light absorption in the visible portion of the solar spectrum. The in vivo conversion from the porphyrin macrocycle in the precursor of Chls, protochlorophyllide a , to the D-ring reduced chlorin ring is regio- and stereoselectively mediated by protochlorophyllide oxidoreductase (POR) 5 – 8 . In photosynthetic bacteria, further hydrogenation of the C7 = C8 double bond in the B-ring of the chlorin macrocycle is mediated by chlorophyllide oxidoreductase (COR) to produce a bacteriochlorin (7,8,17,18-tetrahydroporphyrin), which leads to bacteriochlorophyll (BChl) a (Fig.…”

Construction of a new T7 promoter compatible Escherichia coli Nissle 1917 strain for recombinant production of heme-dependent proteins

“…Several methods have been developed in the past to obtain correctly folded and active proteins loaded with heme cofactor [11,12], however many still do not yield 100% reconstitution with the cofactor. Furthermore, the formation of heme-derived molecules in E. coli, such as phycobilins, is dependent on heme biosynthesis of E. coli cells which is often rate limiting [13]. For the production of higher yields of these molecules, an increased heme availability inside the cell would be an advantage.…”