Largest protein

The largest single-chain protein is PKZILLA-1, with a mass of 4.7 megadaltons, and belongs to the golden alga species Prymnesium parvum. The prodigious protein contains 140 enzyme domains that comprise a total of 45,212 amino acids. The discovery was revealed in a paper published in the journal Science on 8 August 2024.

Lead author of the study, Bradley Moore of the University of California San Diego’s Scripps Institution of Oceanography, described PKZILLA-1 as “the Mount Everest of proteins”.

One dalton is equivalent to the mass of a single hydrogen atom (the lightest element), so PKZILLA-1 is akin to 4.7 million hydrogen atoms.

It is hoped that this discovery may help tackle the growing ecological crisis caused by algal blooms. P. parvum is a particularly problematic alga as it produces the toxin prymnesin which is deadly to fish in both freshwater and saltwater habitats. As this protein plays a key role in the formation of that toxin (in conjunction with another slightly smaller protein dubbed PKZILLA-2, with a mass of 3.2 megadaltons), it may be possible for scientists to now devise methods of detecting and eradicating the algae before the toxin reaches fatal levels. The research may also have applications for material science (e.g., for new forms of fabric) or new drugs that might more effectively combat diseases such as cancer.

PKZILLA-1 surpasses the previous record holder titin (aka connectin), a protein found in human muscles, by 25%; it has a mass of 3.7 megadaltons and is approximately 1 micrometer (0.00004 inch) long. Consisting of about 30,000 amino acids, titin helps to maintain resting tension in muscle tissue and also is instrumental in the contraction of muscle fibres.