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General Function

Trichosurin is a protein from the milk whey of the common brushtail possum Trichosurus vulpecula ^[1]. It is a lipocalin, which is an extracellular protein (17–25 kDa) that can bind and transport small lipophilic molecules ^[2].

Structure

Trichosurin follows the general lipocalin fold pattern, with eight-stranded anti-parallel β-barrel, and the structure then forms a dimer with another identical β-barrel ^[3]. The internal topology of the hydrophobic pocket is a crucial factor in the type and selectivity of binding, as is access to the binding pocket which is usually controlled by residues forming a loop between β-strands at one end of the lipocalin β-barrel.

Structure and Function

The binding site is found in the centre of the β-barrel and can be occupied by water and isopropanol molecules from the corresponding crystallization medium ^[4]. The protein was also crystallized with 2-naphthol and 4-ethylphenol that were bound in the centre of the β-barrel. The presence of such phenolic compounds provides clues to the function of trichosurin- .

Evolutionarily Related Proteins

Trichosurin has significant similarity (34% amino acid identity) to the rodent MUPs (major urinary proteins) and to the major horse dander allergen equ_c1 (28% amino acid identity). Tichosurin homologues have been identified in both the tammar wallaby (87% amino acid identity) and the South American opossum (77% amino acid identity). This high level of conservation in species that diverged approximately 80 million years ago due to continental separation suggests that the function of trichosurin is critical in metatherian lactation.

Relevance

Trichosurin, an important marsupial milk protein, is highly conserved across metatherians. The opossum, a metatherian, shares a common ancestor with humans around 130 million years ago, is of particular importance to study the differences between the development of metatherians and other mammals. In opossums, lactation is divided into three stages that each have a very unique milk composition, and trichosurin is one of three predominant lipocalins found in the milk of T. vulpecula,

Available Structures

References

1. ↑ Watson RP, Demmer J, Baker EN, Arcus VL. Three-dimensional structure and ligand binding properties of trichosurin, a metatherian lipocalin from the milk whey of the common brushtail possum Trichosurus vulpecula. Biochem J. 2007 Nov 15;408(1):29-38. PMID:17685895 doi:10.1042/BJ20070567
2. ↑ Watson RP, Demmer J, Baker EN, Arcus VL. Three-dimensional structure and ligand binding properties of trichosurin, a metatherian lipocalin from the milk whey of the common brushtail possum Trichosurus vulpecula. Biochem J. 2007 Nov 15;408(1):29-38. PMID:17685895 doi:10.1042/BJ20070567
3. ↑ Watson RP, Demmer J, Baker EN, Arcus VL. Three-dimensional structure and ligand binding properties of trichosurin, a metatherian lipocalin from the milk whey of the common brushtail possum Trichosurus vulpecula. Biochem J. 2007 Nov 15;408(1):29-38. PMID:17685895 doi:10.1042/BJ20070567
4. ↑ Watson RP, Demmer J, Baker EN, Arcus VL. Three-dimensional structure and ligand binding properties of trichosurin, a metatherian lipocalin from the milk whey of the common brushtail possum Trichosurus vulpecula. Biochem J. 2007 Nov 15;408(1):29-38. PMID:17685895 doi:10.1042/BJ20070567

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