Glycosyltransferases in the Golgi membranes of onion stem

Powell, Janet T.; Brew, Keith

doi:10.1042/bj1420203

Cited by 47 publications

(12 citation statements)

References 38 publications

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“…While interspecific interactions between a-lac and 13-1,4-galactosyltransferase have been suggested by studies in vitro (20,21), our data provide definitive evidence of function. However, it is not known how efficiently human a-lac forms lactose synthase complex.…”

Section: Discussionsupporting

confidence: 67%

Lactation is disrupted by alpha-lactalbumin deficiency and can be restored by human alpha-lactalbumin gene replacement in mice.

Stacey¹,

Schnieke²,

Kerr³

et al. 1995

Proc. Natl. Acad. Sci. U.S.A.

108

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Mice carrying either a deletion of the murine a-lactalbumin (a-lac) gene (null allele) or its replacement by the human a-lac gene (humanized allele) have been generated by gene targeting. Homozygous null females are a-lacdeficient, produce reduced amounts of thickened milk containing little or no lactose, and cannot sustain their offspring. This provides definitive evidence that a-lac is required for lactose synthesis and that lactose is important for milk production. Females homozygous for the humanized allele lactate normally, indicating that human a-lac can replace murine a-lac. Mouse and human a-lac expression was compared in mice heterozygous for the humanized allele. The human gene expressed "15-fold greater mRNA and "14-fold greater protein than the mouse, indicating that the major determinants of human a-lac expression are close to, or within, the human gene and that the mouse locus does not exert a negative influence on a-lac expression. Variations in a-lac expression levels in nondeficient mice did not affect milk lactose concentration, but the volume of milk increased slightly in mice homozygous for the humanized allele. These variations demonstrated that a-lac expression in mice is gene dosage dependent.Milk is a complex mixture of proteins, lipids, carbohydrates, and inorganic components, the composition of which varies widely between species. The whey protein a-lactalbumin (alac) is thought to influence milk carbohydrate and fluid content through its role as a component of the lactose synthase complex (1). Lactose provides a major osmotic component of milk and determines milk volume by influencing water influx. It has been proposed that the lactose content of milk is directly related to the quantity of a-lac present (2), but a causative relationship has yet to be demonstrated in vivo.We have used gene targeting in embryonic stem cells to produce null and replacement alleles at the murine a-lac locus (3). Mice in which the murine a-lac gene has been completely deleted (null allele) provide a definitive test of the role and importance of a-lac in lactation and mammary physiology. Mice in which the murine a-lac gene has been replaced by the human gene have been used (i) to test whether human a-lac can functionally substitute for mouse a-lac, and (ii) to investigate determinants of a-lac gene expression, since humans and mice produce markedly different amounts of milk a-lac. MATERIALS AND METHODSMouse Lines. Derivation of mice bearing null and humanized a-lac alleles has been described (3).RNA Analysis. Total RNA was prepared from abdominal mammary glands of female mice 5-6 days postpartum. RNase protection analysis used a [32P]CTP-labeled antisense RNA probe transcribed from a 455-bp HindIII-Bal I mouse a-lac fragment (see Fig. 4A) cloned in pBluescript KS. Experimental conditions were as recommended by Promega.Milk Composition and Yield Analysis. Milk samples were collected between days 3 and 7 of lactation. Milk fat content was measured as described by Fleet and Linzell (4). Defatted milk wa...

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Section: Discussionsupporting

confidence: 67%

Lactation is disrupted by alpha-lactalbumin deficiency and can be restored by human alpha-lactalbumin gene replacement in mice.

Stacey¹,

Schnieke²,

Kerr³

et al. 1995

Proc. Natl. Acad. Sci. U.S.A.

108

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“…The apparent K, values for oligosaccharides and ovalbumin (determined at single concentrations of MnZ+ and UDP-galactose) are considerably lower th%n that for free N-acetylglucosamine, which is consistent with the view that they more closely resemble the natural substrates of the enzyme (108,123). The nature of the substituent on the 2 position of the glucopyranose ring appears to be of some importance in determining the properties of monosaccharides as substrates but the ef- In the presence of a-lactalbumin, a distinct change in the specificity of the system for acceptor substrates is observed, which is typified by a reduction in the K , for glucose of 3 orders of magnitude (110,124,125).…”

Section: Ne:y>-gal-gknacsupporting

confidence: 68%

Lactose Synthetase

Hill

Brew

1975

Advances in Enzymology - And Related Areas of Molecular Biology

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“…This raises the intriguing question of how the capability of the snail ,B4-GalNAcT to interact with a-LA has evolved or has been conserved during evolution in the absence of any apparent selective pressure. At present it is hard to answer this question, but it is of interest to note that the property of interacting with a-LA has also been conserved in f34-GalT from chicken, another nonlactating animal (46,58), and in a plant f34-GalT (59).…”

Section: Discussionmentioning

confidence: 99%

Alpha-lactalbumin affects the acceptor specificity of Lymnaea stagnalis albumen gland UDP-GalNAc:GlcNAc beta-R beta 1-->4-N-acetylgalactosaminyltransferase: synthesis of GalNAc beta 1-->4Glc.

Neeleman

Eijnden²

1996

Proc. Natl. Acad. Sci. U.S.A.

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The N,N'-diacetyllactosediamine (lacdiNAc) pathway of complex-type oligosaccharide synthesis is controlled by a UDP-GalNAc:GlcNAcf3-R j81-*4-N-acetylgalactosaminyltransferase (f34-GalNAcT) that acts analogously to the common UDP-Gal:GlcNAcj8-R 131-*4-galactosyltransferase ((34-GaiT). LacdiNAc-based chains particularly occur in invertebrates and cognate ,B4-GalNAcTs have been identified in the snail Lymnaea stagnalis, in two schistosomal species, and in several lepidopteran insect cell lines. Because of the similarity in reactions catalyzed by both enzymes, we investigated whetherL. stagnalis albumen gland (84-GalNAcT would share with mammalian f34-GaIT the property of interacting with a-lactalbumin (c-LA), a protein that only occurs in the lactating mammary gland, to form a complex in which the specificity of the enzyme is changed. It was found that, under conditions where (84-GalT forms the lactose synthase complex with a-LA, the snail .84-GalNAcT was induced by this protein to act on Glc with a > 100-fold increased efficiency, resulting in the formation of the lactose analog GalNAc,81-4Glc. This forms the second example of a glycosyltransferase, the specificity of which can be altered by a modifier protein. So far, however, no protein fraction could be isolated from L. stagnalis that could likewise interact with the 134-GalNAcT. Neither had lysozyme c, a protein that is homologous to a-LA, an effect on the specificity of the enzyme. These results raise the question of how the capability to interact with a-LA has been conserved in the snail enzyme during evolution without any apparent selective pressure. They also suggest that snail (4-GalNAcT and mammalian f84-GalT show similarity at a molecular level and allows the identification of the f34-GalNAcT as a candidate member of the f4-GaIT family.

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Glycosyltransferases in the Golgi membranes of onion stem

Cited by 47 publications

References 38 publications

Lactation is disrupted by alpha-lactalbumin deficiency and can be restored by human alpha-lactalbumin gene replacement in mice.

Lactation is disrupted by alpha-lactalbumin deficiency and can be restored by human alpha-lactalbumin gene replacement in mice.

Lactose Synthetase

Alpha-lactalbumin affects the acceptor specificity of Lymnaea stagnalis albumen gland UDP-GalNAc:GlcNAc beta-R beta 1-->4-N-acetylgalactosaminyltransferase: synthesis of GalNAc beta 1-->4Glc.

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