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Determine Whether a Glycan Is Synthesized by a Given Enzyme

is_synthesized_by.Rd

Glycans are produced through a series of enzymatic reactions. This function checks whether a specific enzyme participates in the biosynthesis of a given glycan (or glycans).

Usage

is_synthesized_by(glycans, enzyme)

Arguments

glycans

A glyrepr::glycan_structure(), or a character vector of glycan structure strings supported by glyparse::auto_parse().

enzyme

An enzyme() or a gene symbol.

Value

A logical vector of the same length as glycans.

Important notes

Here are some important notes for all functions in the glyenzy package.

Applicability

All algorithms and enzyme information in glyenzy are applicable only to humans, and specifically to N-glycans and O-GalNAc glycans. Results may be inaccurate for other types of glycans (e.g., GAGs, glycolipids) or for glycans in other species (e.g., plants, insects).

Inclusiveness

The algorithm takes an intentionally inclusive approach, assuming that all possible isoenzymes capable of catalyzing a given reaction may be involved. Therefore, results should be interpreted with caution.

For example, in humans, detection of the motif "Neu5Ac(a2-3)Gal(b1-" will return both "ST3GAL3" and "ST3GAL4". In reality, only one of them might be active, depending on factors such as tissue specificity.

Only "concrete" glycans

The function only works for glycans containing concrete residues (e.g., "Glc", "GalNAc"), and not for glycans with generic residues (e.g., "Hex", "HexNAc").

Substituents

Subtituents (e.g. sulfation, phosphorylation) is not supported yet, and the algorithms might fail for glycans with subtituents. If your glycans contains substituents, use glyrepr::remove_substituents() to get clean glycans.

Incomplete glycan structures

If the glycan structure is incomplete or partially degraded, the result may be misleading.

Starting points

Throughout glyenzy, the starting glycan is the Glc(3)Man(9)GlcNAc(2) precursor for N-glycans, and GalNAc(a1- for O-glycans. This means that enzymes involved in N-glycan precursor biosynthesis, mainly ALGs, and OST, which transfered the precursor to Asn, are not considered here. Similarly, GALNTs for O-glycans are not considered.

Algorithm

The basic approach is straightforward: for each reaction rule associated with the enzyme, the function checks whether the corresponding product motif appears in the glycan. If any rule matches, the function returns TRUE.

For N-glycans, additional logic is applied to handle special cases. Products of MGAT1 are often further trimmed by glycoside hydrolases, meaning that the final glycan product may no longer contain the original motif. In these cases, the function instead looks for specific motif markers to determine enzyme involvement.

Examples

library(glyrepr)
library(glyparse)

# Use `glycan_structure()` and `enzyme()`
glycan <- auto_parse("Neu5Ac(a2-6)Gal(b1-4)GlcNAc(b1-")
is_synthesized_by(glycan, enzyme("ST6GAL1"))
#> [1] TRUE

# Or use characters directly
is_synthesized_by("Neu5Ac(a2-6)Gal(b1-4)GlcNAc(b1-", "ST6GAL1")
#> [1] TRUE

# Vectorized input
glycans <- c(
  "Neu5Ac(a2-6)Gal(b1-4)GlcNAc(b1-",
  "Gal(b1-4)GlcNAc(b1-"
)
is_synthesized_by(glycans, "ST6GAL1")
#> [1]  TRUE FALSE