4 min read
What is the largest protein?
PKZILLA-1 is the largest known protein at 45,212 amino acids and 4.7 MDa. Titin remains the largest human protein, while dystrophin is much smaller but is encoded by an unusually large gene.
Matic Broz Computational chemist
The largest known protein is PKZILLA-1, a toxin-building enzyme from the golden alga Prymnesium parvum. It contains 45,212 amino acids and was reported in 2024 at 4.7 megadaltons.
The answer changes if the question is narrower. In the human body, the largest protein is titin. In blood plasma, the largest protein-sized object is usually von Willebrand factor because it circulates as very large multimers. Food and industry rankings are different questions because they measure grams of protein or production volume, not amino-acid length or daltons.
What is the longest protein?
The longest known protein by amino-acid sequence is PKZILLA-1, a giant polyketide synthase with 45,212 amino acids.[1][2]
"Longest" counts amino acids in a protein chain, while "largest" usually refers to molecular mass. The two measurements are related but not identical because amino acids have different masses. PKZILLA-1 holds both records: the 2024 study reported a mass of 4.7 MDa, and UniProt calculates 4.76 MDa from its sequence.[1][3]
Its name is short for "PKZILLA-1 giant polyketide synthase," the name used in the UniProt sequence record.[3]
The 2024 Science paper reported 140 enzyme domains in PKZILLA-1 and 99 domains in its companion enzyme PKZILLA-2, which has a reported mass of 3.2 MDa. Together, the enzymes help P. parvum make prymnesin toxins, which are linked to harmful algal blooms and fish kills.[1][2]
| Protein or benchmark | What it answers | Size |
|---|---|---|
| PKZILLA-1 | Largest known protein | 45,212 amino acids; 4.7 MDa reported |
| Titin | Largest human protein | 34,350 amino acids; 3.816 MDa |
| Dystrophin | Large muscle protein, but not the largest | 3,685 amino acids; 426.8 kDa |
| Average eukaryotic protein | Scale reference | 472 amino acids on average |
| Average bacterial protein | Scale reference | 320 amino acids on average |
The table and chart combine reported PKZILLA-1 values from Science, current UniProt sequence records for PKZILLA-1, titin, dystrophin, and von Willebrand factor, and average protein-length estimates from a comparative proteome study.[1][3][4][8][10][12]
Is titin the largest protein in the human body?
Yes. Titin is the largest protein in the human body: the canonical human UniProt sequence has 34,350 amino acids and a molecular mass of 3,816,030 Da.[4]
Titin is encoded by the TTN gene and is also known as connectin. It works in striated muscle, where one titin molecule spans half a sarcomere and helps give muscle its passive elasticity.[5][6]
That makes titin the right answer for "largest protein in the body," "largest human protein," and "scientific name for the largest protein in the human body." The practical scientific name is titin, with gene symbol TTN; the species context is Homo sapiens.[4][6]
Before PKZILLA-1 was reported, titin was commonly described as the largest known protein. It is still the largest well-established human protein, but it is no longer the largest known protein across biology.
Is dystrophin the largest protein?
No. Dystrophin is a large muscle protein, but it is not the largest protein in the human body. The current human dystrophin UniProt sequence has 3,685 amino acids and a molecular mass of 426,778 Da, making titin about nine times longer by amino-acid count.[4][8]
The confusion comes from the DMD gene. NCBI describes DMD as spanning more than 2 Mb of genomic DNA, which makes it an unusually large human gene. But gene length and protein size are different measurements: DMD is a very large gene, while its protein product, dystrophin, is much smaller than titin.[7][8]
What is the largest protein in blood or plasma?
The largest protein in blood plasma is usually von Willebrand factor when it is counted in its circulating multimeric form. Its plasma multimers range from about 500 to 20,000 kDa, far larger than most single-chain proteins.[9]
The individual human von Willebrand factor chain is much smaller than the multimer: UniProt lists 2,813 amino acids and 309,265 Da for the precursor sequence.[10] This is why blood-protein rankings need to say whether they mean a single protein chain or the assembled circulating form.
The plasma chart uses the reported von Willebrand factor multimer range, the UniProt von Willebrand factor precursor mass, and the NCBI Bookshelf fibrinogen mass.[9][10][11]
In basic physiology comparisons of major plasma proteins, fibrinogen is often the largest named plasma protein class. Fibrinogen is a 340 kDa hexameric plasma glycoprotein, while albumin is the most abundant plasma protein but not the largest.[11]
Sources▼
- Giant polyketide synthase enzymes in the biosynthesis of giant marine polyether toxins Science · 2024. https://www.science.org/doi/10.1126/science.ado3290
- Largest protein yet discovered builds algal toxins Scripps Institution of Oceanography · 2024. https://scripps.ucsd.edu/news/largest-protein-yet-discovered-builds-algal-toxins
- PKZILLA-1 UniProtKB entry A0AB34IYJ6 UniProt · July 1, 2026. https://www.uniprot.org/uniprotkb/A0AB34IYJ6/entry
- Titin UniProtKB entry Q8WZ42 UniProt · July 1, 2026. https://www.uniprot.org/uniprotkb/Q8WZ42/entry
- Molecule of the Month: Titin RCSB PDB-101 · 2015. https://pdb101.rcsb.org/motm/185
- TTN titin [Homo sapiens (human)] NCBI Gene · July 1, 2026. https://www.ncbi.nlm.nih.gov/gene/7273
- DMD dystrophin [Homo sapiens (human)] NCBI Gene · July 1, 2026. https://www.ncbi.nlm.nih.gov/gene/1756
- Dystrophin UniProtKB entry P11532 UniProt · July 1, 2026. https://www.uniprot.org/uniprotkb/P11532/entry
- Von Willebrand factor: molecular size and functional activity Annals of Hematology · 1996. https://pubmed.ncbi.nlm.nih.gov/8767102/
- Von Willebrand factor UniProtKB entry P04275 UniProt · July 1, 2026. https://www.uniprot.org/uniprotkb/P04275/entry
- Fibrinogen NCBI Bookshelf · 2025. https://www.ncbi.nlm.nih.gov/books/NBK537184/
- Mathematical modeling and comparison of protein size distribution in different plant, animal, fungal and microbial species reveals a negative correlation between protein size and protein number BMC Research Notes · 2012. https://pmc.ncbi.nlm.nih.gov/articles/PMC3296660/
Founder and computational chemist, ProteinIQ
Dr. Matic Broz is the founder of ProteinIQ and a computational chemist. He completed a PhD focused on protein structure, molecular dynamics, and neural networks, and writes about structural biology and scientific software.