Fut1Edit
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Fut1 (fucosyltransferase 1) is a human gene that encodes an enzyme in the glycosylation pathway responsible for adding fucose, a hexose sugar, to glycan structures on glycoproteins and glycolipids. The resulting α-1,2-fucosylated products are central to the synthesis of the H antigen, which serves as the foundational structure for the ABO blood group system. The activity of Fut1, in concert with related enzymes in the same family, shapes the glycan landscape of red blood cells and mucosal surfaces, influencing not only blood group phenotypes but also cell–cell interactions, pathogen binding, and immune recognition.
Biology and enzymology
Enzymatic function
Fut1 is an alpha-1,2-fucosyltransferase that transfers fucose from GDP-fucose to galactose residues on glycan precursors, generating the H antigen. This reaction establishes the substrate on which the A and B transferases later act to form the distinct ABO antigens. The H antigen exists on red blood cells and also in secretions and mucosal surfaces in individuals with functional FUT1 activity. The biochemical role of Fut1 is therefore foundational to downstream glycosylation processes that influence tissue identity and function. For broader context, see the glycosylation pathway glycosylation and the family of fucosyltransferases fucosyltransferase.
Gene structure and expression
The FUT1 gene is located on chromosome 19 and is part of a gene family that includes other fucosyltransferases. Expression of Fut1 is tissue-specific to varying degrees, with robust activity in erythroid lineage cells and many epithelial and endothelial tissues. The existence of related enzymes that modify similar substrates contributes to a network of glycan modifications that define cellular surfaces. For background on chromosome 19 and gene loci, consult chromosome 19.
Variation and population genetics
Natural variation in FUT1 includes alleles that encode functional or reduced-activity enzymes. Loss-of-function variants in FUT1 can abolish H antigen synthesis in certain cells, leading to rare phenotypes. The most famous example in clinical hematology is the Bombay phenotype (Oh), which results from a lack of H antigen due to nonfunctional FUT1 and a nonfunctional FUT2 in many cases, producing a transfusion phenotype that is incompatible with standard ABO blood group compatibility. For a discussion of related blood group biology, see Bombay phenotype and ABO.
Genetic variation in FUT1 interacts with variation in FUT2, which encodes another fucosyltransferase responsible for H antigen expression in secretions (i.e., secretor status). Together, FUT1 and FUT2 shape the distribution of H antigen across tissues and secretions, influencing both immunohematology and mucosal glycosylation. See secretor status for more on that axis of variation.
Clinical relevance
Transfusion medicine and transplantation
Because ABO phenotyping relies on the presence of H antigen as the substrate for A and B antigen formation, FUT1 status directly impacts blood typing and compatibility testing. Individuals with nonfunctional FUT1 can exhibit altered or absent H antigen expression on red blood cells, which complicates serological typing. In the Bombay phenotype, the absence of H (and thus A and B) antigens leads to the production of anti-H antibodies, creating exceptional requirements for compatible blood supplies. See blood transfusion and Bombay phenotype for related topics.
Infectious disease and host–pathogen interactions
Glycan structures generated by Fut1 contribute to the landscape of host cell surfaces that many pathogens exploit to gain entry or adhere to host tissues. The H antigen, as a carrier of fucose-linked glycans, can influence susceptibility to certain pathogens and the course of infection. In particular, interactions with glycan receptors are relevant in discussions of enteric infections and mucosal immunity; see norovirus and glycobiology for broader context on how glycan variation shapes disease risk.
Cancer biology and cell adhesion
Glycosyltransferases, including Fut1, participate in the modification of glycoproteins and glycolipids that mediate cell–cell adhesion, migration, and signaling. Altered glycosylation patterns have been observed in various cancers, and changes in FUT family expression can correlate with tumor progression in some settings. The field remains active, with debates about the extent to which specific glycan changes drive cancer biology vs. reflect downstream consequences of oncogenic pathways. See cancer biology and glycosylation for related topics.
Evolution and history
FUT1 and related fucosyltransferases are part of a gene family that has diversified across primates and other mammals. Variation in these enzymes can alter tissue glycan patterns in ways that affect host–pathogen interactions, reproductive compatibility, and tissue resilience. Evolutionary analyses consider how selective pressures from infectious agents may shape FUT1/FUT2 alleles across populations. For broader context on selection and human glycan evolution, see natural selection and glycobiology.
Research methods and tools
Investigations into FUT1 employ a range of molecular and biochemical approaches, including sequencing to identify allelic variants, enzymology to characterize catalytic activity, and glycomics to profile the glycan products produced in different tissues. Genome editing tools such as CRISPR are used to model FUT1 function in cell lines or animal models, enabling researchers to dissect tissue-specific roles and pathogen interactions. Analytical techniques in glycoscience, including mass spectrometry and lectin-based assays, help map the distribution of H antigen and related structures.