Physical mapping of the lysozyme gene family in cattle

α-Lactalbumin, Amazing Calcium-Binding Protein

α-Lactalbumin (α-LA) is a small (Mr 14,200), acidic (pI 4–5), Ca²⁺-binding protein. α-LA is a regulatory component of lactose synthase enzyme system functioning in the lactating mammary gland. The protein possesses a single strong Ca²⁺-binding site, which can also bind Mg²⁺, Mn²⁺, Na⁺, K⁺, and some other metal cations. It contains several distinct Zn²⁺-binding sites. Physical properties of α-LA strongly depend on the occupation of its metal binding sites by metal ions. In the absence of bound metal ions, α-LA is in the molten globule-like state. The binding of metal ions, and especially of Ca²⁺, increases stability of α-LA against the action of heat, various denaturing agents and proteases, while the binding of Zn²⁺ to the Ca²⁺-loaded protein decreases its stability and causes its aggregation. At pH 2, the protein is in the classical molten globule state. α-LA can associate with membranes at neutral or slightly acidic pH at physiological temperatures. Depending on external conditions, α-LA can form amyloid fibrils, amorphous aggregates, nanoparticles, and nanotubes. Some of these aggregated states of α-LA can be used in practical applications such as drug delivery to tissues and organs. α-LA and some of its fragments possess bactericidal and antiviral activities. Complexes of partially unfolded α-LA with oleic acid are cytotoxic to various tumor and bacterial cells. α-LA in the cytotoxic complexes plays a role of a delivery carrier of cytotoxic fatty acid molecules into tumor and bacterial cells across the cell membrane. Perhaps in the future the complexes of α-LA with oleic acid will be used for development of new anti-cancer drugs.

Molecular Cloning and Characterization of a New C-type Lysozyme Gene from Yak Mammary Tissue

Milk lysozyme is the ubiquitous enzyme in milk of mammals. In this study, the cDNA sequence of a new chicken-type (c-type) milk lysozyme gene (YML), was cloned from yak mammary gland tissue. A 444 bp open reading frames, which encodes 148 amino acids (16.54 kDa) with a signal peptide of 18 amino acids, was sequenced. Further analysis indicated that the nucleic acid and amino acid sequences identities between yak and cow milk lysozyme were 89.04% and 80.41%, respectively. Recombinant yak milk lysozyme (rYML) was produced by Escherichia coli BL21 and Pichia pastoris X33. The highest lysozyme activity was detected for heterologous protein rYML5 (M = 1,864.24 U/mg, SD = 25.75) which was expressed in P. pastoris with expression vector pPICZαA and it clearly inhibited growth of Staphylococcus aureus. Result of the YML gene expression using quantitative polymerase chain reaction showed that the YML gene was up-regulated to maximum at 30 day postpartum, that is, comparatively high YML can be found in initial milk production. The phylogenetic tree indicated that the amino acid sequence was similar to cow kidney lysozyme, which implied that the YML may have diverged from a different ancestor gene such as cow mammary glands. In our study, we suggest that YML be a new c-type lysozyme expressed in yak mammary glands that plays a role as host immunity.

Genomic organization and evolution of ruminant lysozyme c genes

Ruminant stomach lysozyme is a long established model of adaptive gene evolution. Evolution of stomach lysozyme function required changes in the site of expression of the lysozyme c gene and changes in the enzymatic properties of the enzyme. In ruminant mammals, these changes were associated with a change in the size of the lysozyme c gene family. The recent release of near complete genome sequences from several ruminant species allows a more complete examination of the evolution and diversification of the lysozyme c gene family. Here we characterize the size of the lysozyme c gene family in extant ruminants and demonstrate that their pecoran ruminant ancestor had a family of at least 10 lysozyme c genes, which included at least two pseudogenes. Evolutionary analysis of the ruminant lysozyme c gene sequences demonstrate that each of the four exons of the lysozyme c gene has a unique evolutionary history, indicating that they participated independently in concerted evolution. These analyses also show that episodic changes in the evolutionary constraints on the protein sequences occurred, with lysozyme c genes expressed in the abomasum of the stomach of extant ruminant species showing the greatest levels of selective constraints.

Putative quantitative trait loci associated with the probability of contracting infectious bovine keratoconjunctivitis1,2

Infectious bovine keratoconjunctivitis, also known as pinkeye, is an economically important disease in cattle. The objective of this study was to detect QTL associated with infectious bovine keratoconjunctivitis in offspring from a Brahman x Hereford sire. The sire was mated to Hereford, Angus, and F1 cows to produce 288 offspring in 1994 and mated to MARC III ((1/4) Hereford, (1/4) Angus, (1/4) Red Poll, and (1/4) Pinzgauer) cows in 1996 to produce 259 offspring (547 animals total). Infectious bovine keratoconjunctivitis was diagnosed by physical examination in 36 animals of the family. Records included unilateral and bilateral frequency, but not severity. Records were binary: 0 for unaffected and 1 for affected cattle. A putative QTL for infectious bovine keratoconjunctivitis was identified on chromosome 1, with a maximum F-statistic (F = 10.15; P = 0.0015) at centimorgan 79 of the linkage group. The support interval spanned centimorgans 66 to 110. There was also evidence suggesting the presence of a QTL for infectious bovine keratoconjunctivitis on chromosome 20, with a maximum F-statistic (F = 10.35; P = 0.0014) at centimorgan 16 of the linkage group. The support interval ranged from centimorgan 2 to 35. This report provides the initial evidence of QTL for infectious bovine keratoconjunctivitis. Although a candidate gene was identified for one of the regions of interest, further studies are needed to identify the genetic basis of resistance to the disease.

Structural deviations in a bovine low expression lysozyme-encoding gene active in tissues other than stomach

Lysozyme-encoding genes (Lys) constitute a gene-family in ruminants. While several of these genes are highly expressed in stomach (sLys), few other copies are weakly expressed in other tissues, notably in polymorphnuclear granulocytes and macrophages (mLys). Searching an understanding for these grossly different levels of expression, we isolated the bovine variant of the gene being expressed in granulocytes and characterized it by sequencing, together with its promoter. Spanning about 9 kb of genomic DNA, the gene is found to be segmented into four exons, in common with all other Lys, as known from vertebrates. Sequence homologies between all bovine sLys-variants exceeds 70% over much of the entire coding sequence and promoter region. This indicates (i) that bovine lysozymes expressed either in stomach or granulocyte originate from a common ancestral gene and (ii) also excludes the possibility that the observed weak expression of the mLys gene is due to major structural rearrangements within the promoter segment. However, primer extension analysis based on RNA isolated from kidney locates the transcription startpoint (tsp of that gene) 44 nt further upstream than observed in both, bovine stomach lysozyme RNA or any of the homologous genes in mice and man. The observed weak expression of this bovine mLys gene appears to be a consequence of both the presence of an extra ATG codon in the extended 5'-UTR, and a severe down mutation of the ancestral TATA-box which is only partially compensated for by the presence of another mutation further upstream resulting in a weak substitute promoter sequence.

Insect lysozymes

Lysozymes, related to the chicken-type lysozymes in vertebrates, are ubiquitous components in the bacteriolytic armamentarium of insects. The enzyme is normally present in the blood, and together with other bactericidal factors lysozyme is often strongly induced when the insect is infected. This response is regulated by mechanisms that are related to those that activate inflammatory, acute-phase and immune responses in mammals, and the induction of lysozyme and other factors is now being investigated as a model for innate immune reactions in general. A special adaptation is seen in flies like Musca and Drosophila. These animals live on the microorganisms in decompositing matter, and they have developed a specialized set of lysozymes that are expressed in the alimentary tract. In Drosophila, at least seven different lysozyme genes are clustered in a small region on the third chromosome. The different genes are expressed in different parts of the digestive tract, and at different time points during development, and they are highly divergent in sequence. The major lysozymes in the fly gut have acidic isoelectric points and/or pH optima, and their evolution provides an interesting parallel to the ruminants.

Molecular evolution of ruminant lysozymes

The evolution of a new digestive enzyme, stomach lysozyme, from an antibacterial host defense enzyme provides a link between molecular evolution and organismal evolution. Lysozymes have been recruited at least three times (twice from a conventional lysozyme c and once from a calcium-binding lysozyme c) in vertebrates for functioning in the stomach. The recruitment of lysozyme for its new biological function involved many molecular changes, beyond those required to adapt the protein to function in the stomach. The evolution of the stomach lysozyme gene has been extensively studied in ruminant artiodactyls. In ruminants, the lysozyme c gene has duplicated to yield a family of about ten genes. These duplications allowed: (1) specialization of gene function and (2) increased levels of expression. The ruminant stomach lysozyme genes have evolved in an episodic fashion - there was a period of rapid adaptive sequence evolution, driven by positive selection in the early ruminant, that was followed by an increase in purifying selection upon the well-adapted stomach lysozyme sequence among modern species. Recombination of small portions (exons) of the genes between members of the lysozyme gene family may have aided in adaptive evolution. Evolution to a stomach lysozyme is not irreversible; at least one member of the ruminant stomach lysozyme gene family appears to have reverted to a more ancestral function, yet retains hallmarks of its history as a stomach lysozyme.

Isolation and characterization of vertebrate lysozyme genes

Lysozyme genes have been model genes in molecular genetics. The chicken lysozyme c gene was among the first genes to be isolated and characterized, but since then, many other members of the lysozyme gene family have been isolated and characterized. Of all the members of the gene family, the conventional lysozyme c gene has been the most extensively studied at the molecular level. General properties of members of the lysozyme gene family are that they are relatively small genes of less than 10 kilobases in length, and are made up of four exons and three introns. There has been a long history of gene duplication events within the lysozyme gene family, and in several cases, eg., stomach lysozymes, this has led to the evolution of novel biological functions. Initially the structure of the lysozyme c gene appeared to support the exon theory of genes, but the recent characterization of additional lysozymes shows that the predictions of this theory are not supported. Lysozyme genes continue to yield new insights into the molecular processes moulding the vertebrate genome.

Somatic cell mapping of conglutinin (CGN1) to cattle syntenic group U29 and fluorescence in situ localization to Chromosome 28

A 260-bp genomic PstI fragment, which encodes a portion of the carbohydrate recognition domain, was used along with hybrid somatic cells to map the conglutinin gene (CGN1) to domestic cow (Bos taurus) syntenic group U29. In turn, a cosmid containing the entire bovine CGN1 was used with fluorescence in situ hybridization to sublocalize this gene to cattle Chromosome (Chr) (BTA) 28 band 18. Since BTA 28 and several of the other small acrocentric autosomes of cattle are difficult to discriminate, we have also chromosomally sublocalized CGN1 to the p arm of the lone biarmed autosome of the gaur (Bos gaurus). The use of the gaur 2/28 Robertsonian as a marker chromosome and our assignment of CGN1 to BTA 28 should help resolve some of the nomenclatural questions involving this cattle chromosome.

Chromosomal localization of the lysozyme gene cluster in river buffalo (Bubalus bubalis L.)

Lysozyme (LYZ) is an antibacterial enzyme which allows the digestion of bacteria present in tears and saliva. In the true stomach of ruminants LYZ breaks open the bacteria of the foregut, which are subsequently digested by typical mammalian digestive enzymes, allowing the incorporation of nutrients from the bacteria. Southern analysis with a single exon from a cow lysozyme gene revealed that there are about 10 genes in ruminants (Irwin & Wilson 1989), while pig and primates have a single lysozyme gene (Swanson et al. 1991) and camels have two (Irwin et al. 1992). The higher number of LYZ genes in ruminants is believed to be the result of gene duplication associated with the evolution of foregut fermentation (Irwin et al. 1992). Recently, the genomic organization of the lysozyme gene family has been determined in domestic cattle, and, using a cocktail of genomic clones, the lysozyme gene cluster (LYZ/) was assigned to chromosome (Chr) 5, band 23 by fluorescence in situ hybridization (FISH) (Gallagher et al. 1993). In our continued effort to test the genetic homology of conserved chromosome banding regions between cattle and river buffalo, and to extend the river buffalo physical gene map, we have mapped the LYZ/ by FISH and R-banding.