Abstract
The neural cell adhesion molecule and the voltage-sensitive sodium channel alpha-subunit are the only two molecules in mammals known to be modified by alpha-2,8-linked polysialic acid (polySia). We found a new polySia-containing glycoprotein in human milk and identified it as CD36, a member of the B class of the scavenger receptor superfamily. The polySia-containing glycan chain(s) were removed by alkaline treatment but not by peptide:N-glycanase F digestion, indicating that milk CD36 contained polySia on O-linked glycan chain(s). Polysialylation of CD36 occurs not only in human milk but also in mouse milk. However, CD36 in human platelets is not polysialylated. PolySia CD36 is secreted in milk at any lactation stage and reaches peak level at 1 month after parturition. Thus, it is suggested that polySia of milk CD36 is significant for neonatal development in terms of protection and nutrition.
Highlights
The neural cell adhesion molecule and the voltagesensitive sodium channel ␣-subunit are the only two molecules in mammals known to be modified by ␣-2,8linked polysialic acid
An intermediate size of sialyl chains between monoSia and polysialic acid (polySia) occurs extensively in various glycoproteins in mammals [12, 22, 23, 25,26,27]. This class of sialyl groups consists of diSia and oligoSia with up to seven sialic acids (Sia) residues and is present in functionally important glycoproteins, such as adiponectin, which is involved in energy consumption in obesity; CD166, which is involved in neurite extension and T cell activation; and integrin, which is involved in cell-matrix interactions
Detection of PolySia in Human Milk by Chemical Methods—We previously demonstrated that several glycoproteins in brain, adipose tissue, and blood have the diSia and oligoSia structures [12, 22, 23, 25,26,27]
Summary
Sialic acids; Neu5AC, N-acetylneuraminic acid; polySia, polysialic acid; DP, degree of polymerization; BSA, bovine serum albumin; diSia, disialic acid; NCAM, neural cell adhesion molecules; Endo-N, Endo-N-acylneuraminidase; mAb, monoclonal antibody; DMB, 1,2-diamino-4,5-methylenedioxybenzene; PNGase F, peptide:N-glycanase; oligoSia, oligosialic acid; PBS, phosphatebuffered saline; gp, glycoprotein; PVDF, polyvinylidene difluoride; ST8Sia, ␣-2,8-sialyltransferase; BSA, bovine serum albumin. This class of sialyl groups consists of diSia and oligoSia with up to seven Sia residues and is present in functionally important glycoproteins, such as adiponectin, which is involved in energy consumption in obesity; CD166, which is involved in neurite extension and T cell activation; and integrin, which is involved in cell-matrix interactions The study of these novel structures is possible because of the recently developed, highly sensitive detection techniques [12, 28, 29] including fluorometric high performance liquid chromatography and anti-di/oligo/polySia antibodies with defined specificity.
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