Yeast protein

The mmen is not functional at birth and milk is shunted to the abomasum. One to two weeks after birth, the neonate consumes soHd food if offered. A calf or lamb that is nursing tends to nibble the mother s feed. An alternative method of raising the neonate is to remove it from its mother at a very young age, <1 week. A common example of an early weaning situation is the dairy calf that is removed from the cow soon after birth so that the cow s milk supply might be devoted entirely to production. In this instance, the neonate requires complete dietary supplementation with milk replacer. Sources of milk replacer protein have traditionally included milk protein but may also include soybean proteins, fish protein concentrates, field bean proteins, pea protein concentrates, and yeast protein (4). Information on the digestibiUty of some of these protein sources is available (4). 

Yeast. The advantages of expression in yeast include potentially high level production of proteins, the abiUty to have expressed proteins secreted into the media for ease of purification, and relatively low cost, easy scale-up. A disadvantage is that plasmid instabiUty may be a problem which can lead to low product yield. Whereas post-translational modification occurs in yeast, proteins are quite often hyperglycosylated. This is generally a problem with expression in Saccharomyces cerevisiae but not for the more recently used yeast host Pichiapastoris (25) (see Yeasts). 

Filtering. Conditioning or 1 agering gives the beer its desired organoleptic properties, but it stiU contains yeast, protein-tannin complexes, etc, ie, it has a hazy appearance. A high quaHty beer must be clear and totaUy sterile, have coUoidal stabiHty, and yeast must be removed to aUow the beer to have biological stabiHty. The protein-tannin complexes must also be removed so as not to upset the coUoidal stabiHty. 

In terms of amino acids bacterial protein is similar to fish protein. The yeast s protein is almost identical to soya protein fungal protein is lower than yeast protein. In addition, SCP is deficient in amino acids with a sulphur bridge, such as cystine, cysteine and methionine. SCP as a food may require supplements of cysteine and methionine whereas they have high levels of lysine vitamins and other amino acids. The vitamins of microorganisms are primarily of the B type. Vitamin B12 occurs mostly hi bacteria, whereas algae are usually rich in vitamin A. The most common vitamins in SCP are thiamine, riboflavin, niacin, pyridoxine, pantothenic acid, choline, folic acid, inositol, biotin, B12 and P-aminobenzoic acid. Table 14.4 shows the essential amino acid analysis of SCP compared with several sources of protein. 

From a genetical point of view, Saccharomyces cerevisiae is an ideal organism which may be considered the Escherichia coli of eukaryotic cells [4,5]. This is true in particular for the study of metabolic regulation and for that of membrane transport [6]. Finally, the astonishing resemblance between many yeast proteins and certain mammalian-cell proteins has seriously broadened the scope of interest. Although a few reports have appeared on amino acid transport in some other yeasts, most investigations in this field have used strains of Saccharomyces cerevisiae. 

Kinoshita, N., Yamano, H., Niwa, H Yoshida, T., and Yanagida, M. (1993). Negative regulation of mitosis by the fission yeast protein phosphatase ppa2. Genes Dev. 7 1059-1071. 

Nakielny, S., Campbell, D. G., and Cohen, P. (1992b). MAP kinase kinase from rabbit skeletal muscle a novel dual specificity enzyme showing homology to yeast protein kinases involved in pheromone-dependent signal transduction. FEBS Lett. 308 183-189. 

The ratio of peaks for peptides derived from 42 high abundance yeast proteins was examined for the wild type versus cln2 mutant strains (Oda et al., 1999). Only two of the proteins, a peroxisomal membrane protein and S-adenosylmethionine synthase 2, exhibited significant differences in expression between the strains. The biological significance of this observation is not yet known but the study does indicate that changes of >20% in expression levels can be detected using the technique (Oda et al., 1999). 

Figure 5.4. Example of a small region of a hypothetical protein interaction network. Each letter represents a different yeast protein. The white boxes and gray boxes represent genes that are involved in the same function while the hatched boxes indicate proteins of unknown function. The A protein is likely to be involved in the same process as the white box protein and the J protein is likely to be involved in the same process as the gray box proteins because of the multiple interactions within the network. The connection between the E and I proteins indicates communication between the cellular processes. Figure adapted from Hazbun and Fields (2001).

Ito, T., Chiba, T., Ozawa, R., Yoshida, M., Hattori, M., and Sakaki, Y. (2001). A comprehensive two-hybrid analysis to explore the yeast protein interactome. Proc. Natl. Acad. Sci. USA 98, 4569-4574. 

Ito T et al. A comprehensive two-hybrid analysis to explore the yeast protein inter-actome. Proc Natl Acad Sci USA 2001 98 4569-4574. 

Zhu H et al. Analysis of yeast protein kinases using protein chips. Nature Genet 2000 26 283-289. 

Norbeck J et al. Two-dimensional electrophoretic separation of yeast proteins using a non-linear wide range (pH 3-10) immobilized pH gradient in the first dimension reproducibility and evidence for isoelectric focusing of alkaline (pi >7) proteins. Yeast 1997 13 1519-1534. 

Guerrero et al. (2006) used this technique along with the quantitative mass spec strategy called SILAC (stable isotope labeling of amino acids in cell culture Ong et al., 2002) to identify the yeast proteins that interact with the 26 S proteasome. 

Domain Definition Phyletic distribution Yeast proteins (domains) Worm proteins (domains) PDB... 

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