The localization and multimeric nature of component PP3 in bovine milk: purification and characterization of PP3 from caprine and ovine milks

Whey proteins as multifunctional food materials: Recent advancements in hydrolysis, separation, and peptidomimetic approaches

Whey protein derived bioactives, including α-lactalbumin, ß-lactoglobulin, bovine serum albumin, lactoferrin, transferrin, and proteose-peptones, have exhibited wide ranges of functional, biological and therapeutic properties varying from anticancer, antihypertensive, and antimicrobial effects. In addition, their functional properties involve gelling, emulsifying, and foaming abilities. For these reasons, this review article is framed to understand the relationship existed in between those compound levels and structures with their main functional, biological, and therapeutic properties exhibited either in vitro or in vivo. The impacts of hydrolysis mechanism and separation techniques in enhancing those properties are likewise discussed. Furthermore, special emphasize is given to multifunctional effects of whey derived bioactives and their future trends in ameliorating further food, pharmaceutical, and nutraceutical products. The underlying mechanism effects of those properties are still remained unclear in terms of activity levels, efficacy, and targeted effectiveness. For these reasons, some important models linking to functional properties, thermal properties and cell circumstances are established. Moreover, the coexistence of radical trapping groups, chelating groups, sulfhydryl groups, inhibitory groups, and peptide bonds seemed to be the key elements in triggering those functions and properties. Practical Application: Whey proteins are the byproducts of cheese processing and usually the exploitation of these food waste products has increasingly getting acceptance in many countries, especially European countries. Whey proteins share comparable nutritive values to milk products, particularly on their richness on important proteins that can serve immune protection, structural, and energetic roles. The nutritive profile of whey proteins shows diverse type of bioactive molecules like α-lactalbumin, ß-lactoglobulin, lactoferrin, transferrin, immunoglobulin, and proteose peptones with wide biological importance to the living system, such as in maintaining immunological, neuronal, and signaling roles. The diversification of proteins of whey products prompted scientists to exploit the real mechanisms behind of their biological and therapeutic effects, especially in declining the risk of cancer, tumor, and further complications like diabetes type 2 and hypertension risk effects. For these reasons, profiling these types of proteins using different proteomic and peptidomic approaches helps in determining their biological and therapeutic targets along with their release into gastrointestinal tract conditions and their bioavailabilities into portal circulation, tissue, and organs. The wide applicability of those protein fractions and their derivative bioactive products showed significant impacts in the field of emulsion and double emulsion stabilization by playing roles as emulsifying, surfactant, stabilizing, and foaming agents. Their amphoteric properties helped them to act as excellent encapsulating agents, particularly as vehicle for delivering important vitamins and bioactive compounds. The presence of ferric elements increased their transportation to several metal-ions in the same time increased their scavenging effects to metal-transition and peroxidation of lipids. Their richness with almost essential and nonessential amino acids makes them as selective microbial starters, in addition their richness in sulfhydryl amino acids allowed them to act a cross-linker in conjugating further biomolecules. For instance, conjugating gold-nanoparticles and fluorescent materials in targeting diseases like cancer and tumors in vivo is considered the cutting-edges strategies for these versatile molecules due to their active diffusion across-cell membrane and the presence of specific transporters to these therapeutic molecules.

Digestibility of proteins in camel milk in comparison to bovine and human milk using an in vitro infant gastrointestinal digestion system

The absence of β-lactoglobulin, high β-/α_s-casein ratio and protective proteins make camel milk a promising alternative protein base for making human infant formulae. In this study, protein digestibility of camel milk was compared with that of bovine and human milk using an in vitro infant gastrointestinal digestion system. A low degree of gastric proteolysis was observed in all three kinds of milk, and a single clot was formed in camel milk. The soluble milk proteins remaining in the gastric digesta were digested rapidly and extensively in the intestinal phase, while the proteins in the camel milk clot were hydrolysed gradually. Despite several similarities, bioactive peptides unique to individual milk were identified in the three intestinal milk digesta. The results suggest that camel milk proteins are equally digestible as bovine and human milk proteins under infant gastrointestinal digestion conditions, and it may be a prospective substitute for infant formula base.

Variations in N-linked glycosylation of glycosylation-dependent cell adhesion molecule 1 (GlyCAM-1) whey protein: Intercow differences and dietary effects

In bovine milk serum, the whey proteins with the highest N-glycan contribution are lactoferrin, IgG, and glycosylation-dependent cellular adhesion molecule 1 (GlyCAM-1); GlyCAM-1 is the dominant N-linked glycoprotein in bovine whey protein products. Whey proteins are base ingredients in a range of food products, including infant formulas. Glycan monosaccharide composition and variation thereof may affect functionality, such as the interaction of glycans with the immune system via recognition receptors. It is therefore highly relevant to understand whether and how the glycosylation of whey proteins (and their functionality) can be modulated. We recently showed that the glycoprofile of GlyCAM-1 varies between cows and during early lactation, whereas the glycoprofile of lactoferrin was highly constant. In the current study, we evaluated intercow differences and the effects of macronutrient supply on the N-linked glycosylation profiles of the major whey proteins in milk samples of Holstein-Friesian cows. Overall, approximately 60% of the N-glycan pool in milk protein was sialylated, or fucosylated, or both; GlyCAM-1 contributed approximately 78% of the total number of glycans in the overall whey protein N-linked glycan pool. The degree of fucosylation ranged from 44.8 to 73.3% between cows, and this variation was mainly attributed to the glycans of GlyCAM-1. Dietary supplementation with fat or protein did not influence the overall milk serum glycoprofile. Postruminal infusion of palm olein, glucose, and essential AA resulted in shifts in the degree of GlyCAM-1 fucosylation within individual cows, ranging in some cases from 50 to 71% difference in degree of fucosylation, regardless of treatment. Overall, these data demonstrate that the glycosylation, and particularly fucosylation, of GlyCAM-1 was variable, although these shifts appear to be related more to individual cow variation than to nutrient supply. To our knowledge, this is the first report of variation in glycosylation of a milk glycoprotein in mature, noncolostral milk. The functional implications of variable GlyCAM-1 fucosylation remain to be investigated.

NMR structural studies and mechanism of action of Lactophoricin analogs as antimicrobial peptides

Antimicrobial peptides (AMPs) are effective alternatives to conventional antibiotics. They protect the host from the constant invasion of a broad range of infectious microorganisms. AMPs have been at the forefront of the response to multidrug-resistant microbial strains and appear to be ideal drug candidates. Lactophoricin (LPcin), naturally produced from bovine milk, is a typical cationic antimicrobial peptide. Three analog peptides, including LPcin-YK5, LPcin-YK8, and LPcin-YK11, with enhanced antimicrobial activity compared to the wild-type LPcin, were designed and expressed in our laboratory. We investigated the structure and antimicrobial mechanisms of action of the three novel antimicrobial peptide analogs derived from LPcin using solution NMR and solid-state NMR spectroscopy in membrane environments. Our results revealed that the three LPcin analogs exhibited helical structures with different tilt angles on the phospholipid membrane surface. We proposed three-dimensional conformations and antibacterial mechanisms of action of the three peptide analogs in the phospholipid bilayers using two-dimensional solid-state separated local field NMR experiments.

In Depth Analysis of the Contribution of Specific Glycoproteins to the Overall Bovine Whey N-Linked Glycoprofile

The N-linked glycoprofile of bovine whey is the combined result of individual protein glycoprofiles. In this work, we provide in-depth structural information on the glycan structures of known whey glycoproteins, namely, lactoferrin, lactoperoxidase, α-lactalbumin, immunoglobulin-G (IgG), and glycosylation-dependent cellular adhesion molecule 1 (GlyCAM-1, PP3). The majority (∼95%) of N-glycans present in the overall whey glycoprofile were attributed to three proteins: lactoferrin, IgG, and GlyCAM-1. We identified specific signature glycans for these main proteins; lactoferrin contributes oligomannose-type glycans, while IgG carries fucosylated di-antennary glycans with Gal-β(1,4)-GlcNAc (LacNAc) motifs. GlyCAM-1 is the sole whey glycoprotein carrying tri- and tetra-antennary structures, with a high degree of fucosylation and sialylation. Signature glycans can be used to recognize individual proteins in the overall whey glycoprofile as well as for protein concentration estimations. Application of the whey glycoprofile analysis to colostrum samples revealed dynamic protein concentration changes for IgG, lactoferrin, and GlyCAM-1 over time.

The protein and lipid composition of the membrane of milk fat globules depends on their size

In bovine milk, fat globules (MFG) have a heterogeneous size distribution with diameters ranging from 0.1 to 15 µm. Although efforts have been made to explain differences in lipid composition, little is known about the protein composition of MFG membranes (MFGM) in different sizes of MFG. In this study, protein and lipid analyses were combined to study MFG formation and secretion. Two different sized MFG fractions (7.6±0.9 µm and 3.3±1.2 µm) were obtained by centrifugation. The protein composition of MFGM in the large and small MFG fractions was compared using mass-spectrometry-based proteomics techniques. The lipid composition and fatty acid composition of MFG was determined using HPLC-evaporative light-scattering detector and gas chromatography, respectively. Two frequently studied proteins in lipid droplet biogenesis, perilipin-2 and TIP47, were increased in the large and small MFG fractions, respectively. In the large MFG fraction, besides perilipin-2, cytoplasmic vesicle proteins (heat shock proteins, 14-3-3 proteins, and Rabs), microfilaments and intermediate filament-related proteins (actin and vimentin), host defense proteins (cathelicidins), and phosphatidylinositol were higher in concentration. On the other hand, cholesterol synthesis enzymes [lanosterol synthase and sterol-4-α-carboxylate 3-dehydrogenase (decarboxylating)], cholesterol, unsaturated fatty acids, and phosphatidylethanolamine were, besides TIP47, higher in concentration in the small MFG fraction. These results suggest that vesicle proteins, microfilaments and intermediate filaments, cholesterol, and specific phospholipids play an important role in lipid droplet growth, secretion, or both. The observations from this study clearly demonstrated the difference in protein and lipid composition between small and large MFG fractions. Studying the role of these components in more detail in future experiments may lead to a better understanding of fat globule formation and secretion.

Structural and functional characteristics of bovine milk protein glycosylation

Most secreted and cell membrane proteins in mammals are glycosylated. Many of these glycoproteins are also prevalent in milk and play key roles in the biomodulatory properties of milk and ultimately in determining milk's nutritional quality. Although a significant amount of information exists on the types and roles of free oligosaccharides in milk, very little is known about the glycans associated with milk glycoproteins, in particular, the biological properties that are linked to their presence. The main glycoproteins found in bovine milk are lactoferrin, the immunoglobulins, glycomacropeptide, a glycopeptide derived from κ-casein, and the glycoproteins of the milk fat globule membrane. Here, we review the glycoproteins present in bovine milk, the information currently available on their glycosylation and the biological significance of their oligosaccharide chains.

Proteolytic activation of proteose peptone component 3 by release of a C-terminal peptide with antibacterial properties

The milk protein proteose peptone component 3 (PP3, also known as lactophorin) is a small phosphoglycoprotein, which is exclusively expressed in the lactating mammary gland. A 23-residue synthetic peptide (lactophoricin, Lpcin S), corresponding to the C-terminal amphipathic α-helix of PP3, has previously been shown to permeabilize membranes and display antibacterial activity. Lactophorin readily undergoes proteolytic cleavage in milk and during dairy processing, and it has been suggested that PP3-derived peptides are part of milk's endogenous defense system against bacteria. Here, we report that a 26-residue C-terminal peptide (Lpcin P) can be generated by trypsin proteolysis of PP3 and that structural and functional studies of Lpcin P indicate that the peptide has antibacterial properties. The Lpcin P showed α-helical structure in both anionic and organic solvents, and the amount of α-helical structure was increased in the presence of lipid vesicles. Oriented circular dichroism showed that Lpcin P oriented parallel to the membrane surface. However, the peptide permeabilized calcein-containing vesicles efficiently. Lpcin P displayed antibacterial activity against Streptococcus thermophilus, but not against Staphylococcus aureus and Escherichia coli. The PP3 full-length protein did not display the same properties, which could indicate that PP3 functions as a precursor protein that upon proteolysis, releases a bioactive antibacterial peptide.

PP3 forms stable tetrameric structures through hydrophobic interactions via the C-terminal amphipathic helix and undergoes reversible thermal dissociation and denaturation

The milk protein proteose peptone component 3 (PP3), also called lactophorin, is a small phosphoglycoprotein that is expressed exclusively in lactating mammary tissue. The C-terminal part of the protein contains an amphipathic helix, which, upon proteolytic liberation, shows antibacterial activity. Previous studies indicate that PP3 forms multimeric structures and inhibits lipolysis in milk. PP3 is the principal component of the proteose peptone fraction of milk. This fraction is obtained by heating and acidifying skimmed milk, and in the dairy industry milk products are also typically exposed to treatments such as pasteurization, which potentially could result in irreversible denaturation and inactivation of bioactive components. We show here, by the use of CD, that PP3 undergoes reversible thermal denaturation and that the α-helical structure of PP3 remains stable even at gastric pH levels. This suggests that the secondary structure survives treatment during the purification and possibly some of the industrial processing of milk. Finally, asymmetric flow field-flow fractionation and multi-angle light scattering reveal that PP3 forms a rather stable tetrameric complex, which dissociates and unfolds in guanidinium chloride. The cooperative unfolding of PP3 was completely removed by the surfactant n-dodecyl-β-d-maltoside and by oleic acid. We interpret this to mean that the PP3 monomers associate through hydrophobic interactions via the hydrophobic surface of the amphipathic helix. These observations suggest that PP3 tetramers act as reservoirs of PP3 molecules, which in the monomeric state may stabilize the milk fat globule.

Invited review: physiological properties of bioactive peptides obtained from whey proteins

Processing of whey proteins yields several bioactive peptides that can trigger physiological effects in the human body: on the nervous system via their opiate and ileum-contracting activities; on the cardiovascular system via their antithrombotic and antihypertensive activities; on the immune system via their antimicrobial and antiviral activities; and on the nutrition system via their digestibility and hypocholesterolemic effects. The specific physiological effects, as well the mechanisms by which they are achieved and the stabilities of the peptides obtained from various whey fractions during their gastrointestinal route, are specifically discussed in this review.

Cloning, expression, isotope labeling, purification, and characterization of bovine antimicrobial peptide, lactophoricin in Escherichia coli

Lactophoricin (LPcin-I) is a 23-amino acid peptide that corresponds to the carboxyterminal 113-135 region of component-3 of proteose peptone (PP3), a minor phosphoglycoprotein found in bovine milk. It has been reported that lactophoricin has antibacterial activity and a cationic amphipathic helical structure, but its shorter analogous peptide (LPcin-II), a 17-amino acid peptide, corresponding to the 119-135 region of PP3 does not display antibacterial activity. LPcin-I and LPcin-II have similar charge ratios and identical hydrophobic/hydrophilic sectors, according to their helical wheel projection patterns, and both peptides show cationic amphipathic helical folding and interact with membranes. However, it is known that only LPcin-I incorporates into planar lipidic bilayers to form voltage-dependent channels. In this study, the authors cloned and expressed the two recombinant peptides as ketosteroid isomerase (KSI) fusion proteins inclusion bodies in Escherichia coli. These peptides were subjected to NMR structural studies to explore their structure-activity relationships. Fusion proteins were purified by Ni-NTA affinity chromatography under denaturing conditions, and recombinant LPcin-I and LPcin-II were released from fusion by CNBr cleavage. Final purifications of LPcin-I and LPcin-II were achieved by preparative reversed-phase high performance liquid chromatography. Using these methods, we obtained several tens of milligrams of uniformly and selectively (15)N labeled peptides per liter of growth, which was sufficient for solid-state NMR spectroscopy. Peptides were identified by tris-tricine polyacrylamide gel electrophoresis and HSQC spectra. Initial structural data were obtained by solution NMR spectroscopy and compared in membrane-like environments.

Thermocalcic Aggregation of Milk Fat Globule Membrane Fragments from Acid Buttermilk Cheese Whey

Fragments originating from the milk fat globule membrane (MFGM), which is rich in polar lipids and membrane-specific proteins, are gaining interest for their functional and nutritional properties. Acid buttermilk cheese whey was used as a source for MFGM purification, because its MFGM content is more than 5 times higher than that of standard rennet whey. Because polar lipids are the main constituent of the MFGM and only occur in membranous structures, the polar lipid content was taken as a parameter for the total MFGM fragment content. The process of thermocalcic aggregation was evaluated on its recovery of MFGM fragments in the pellet. This method, originally intended for whey clarification and defatting, is a combination of calcium addition, a pH increase, and a thermal treatment. The influence of pH (6.5 to 8), temperature (40 to 70 degrees C), and calcium concentration (0.1 to 0.24 g/100 g) on the pellet mass and dry matter (DM) content and on recovery of protein and polar lipids (and thus indirectly on MFGM fragments) was investigated by means of a response surface Box-Behnken orthogonal design. Reduced quadratic models were fit to the experimental data and were found to be highly significant. No outliers were observed. The recovery of MFGM fragments was found to be highly dependent on the pH, and less dependent on temperature and calcium addition. Next to MFGM proteins, whey proteins were also found to be involved in the formation of aggregates. Optimal conditions were found at 55 degrees C, pH 7.7, and 0.205 g of calcium/L of whey. Under these conditions, 91.0% of the whey polar lipids were recovered in a firm and compact pellet of only 7.86% of the original whey mass, with a polar lipid concentration of 8.34% on pellet DM. Washing with water and centrifugation of the pellet was successful because after one washing step, virtually all sugars were removed, whereas 75.9% of the whey polar lipids could still be recovered. As such, the polar lipid content of the washed pellet increased to 10.70% on a DM basis. However, a second washing step resulted in serious losses of MFGM material.

Filtration of Milk Fat Globule Membrane Fragments from Acid Buttermilk Cheese Whey

The proteins and polar lipids present in milk fat globule membrane (MFGM) fragments are gaining attention for their technological and nutritional properties. These MFGM fragments are preferentially enriched in side streams of the dairy industry, like butter serum, buttermilk, and whey. The objective of this study was to recover MFGM fragments from whey by tangential filtration techniques. Acid buttermilk cheese whey was chosen as a source for purification by tangential membrane filtration because it is relatively rich in MFGM-fragments and because casein micelles are absent. Polyethersulfone and cellulose acetate membranes of different pore sizes were evaluated on polar lipid and MFGM-protein retention upon filtration at 40 degrees C. All fractions were analyzed for dry matter, ash, lipids, proteins, reducing sugars, polar lipid content by HPLC, and for the presence of MFGM proteins by sodium dodecyl sulfate-PAGE. A fouling coefficient was calculated. It was found that a thermocalcic aggregation whey pretreatment was very effective in the clarification of the whey, but resulted in low permeate fluxes and high retention of ash and whey proteins. By means of an experimental design, the influence of pH and temperature on the fouling and the retention of polar lipids (and thus MFGM fragments), proteins, and total lipids upon microfiltration with 0.15 microM cellulose acetate membrane was investigated. All models were highly significant, and no outliers were observed. By increasing the pH from 4.6 to 7.5, polar lipid retention at 50 degrees C increased from 64 to 98%, whereas fouling of the filtration membrane was minimized. A 3-step diafiltration of acid whey under these conditions resulted in a polar lipid concentration of 6.79 g/100 g of dry matter. As such, this study shows that tangential filtration techniques are suited for the purification of MFGM fragments.

Antibacterial Activity of Lactophoricin, a Synthetic 23-Residues Peptide Derived from the Sequence of Bovine Milk Component-3 of Proteose Peptone

A synthetic peptide of 23 residues corresponding to the carboxyterminal 113 to 135 region of component-3 of proteose peptone (PP3) has been investigated with regard to its antibacterial properties. This cationic amphipathic peptide that we refer to as lactophoricin, displayed a growth-inhibitory activity against both gram-positive and gram-negative bacteria. For most of the strains tested, bacterial growth was observed in the presence of lactophoricin except for Streptococcus thermophilus. In that case, lactophoricin exhibited a minimum inhibitory concentration of 10 microM and a minimum lethal concentration of 20 microM. No hemolysis of human red blood cells was detected for peptide concentrations between 2 to 200 microM, indicating that lactophoricin would be noncytotoxic when used in this concentration range.

Evidence for membrane affinity of the C-terminal domain of bovine milk PP3 component

Component PP3 is a phosphoglycoprotein isolated from bovine milk with unknown biological function, which displays in its C-terminal region a basic amphipathic alpha-helix, a feature often involved in membrane association. According to that, the behaviour of PP3 and of a synthetic peptide from the C-terminal domain (residues 113-135) was investigated in lipid environment. Conductance measurements indicated that the peptide was able to associate and form channels in planar lipid bilayers composed of neutral or charged phospholipids. Electrostatic interactions seemed to promote voltage-dependent channel formation but this was not absolutely required since the pore-forming ability of the 113-135 C-terminal peptide was also detected with the zwitterionic lipid bilayer. Additionally, a spectroscopic study using circular dichroism argues that the peptide adopts an alpha-helical conformation in interaction with neutral or charged micelles. Thus, the conducting aggregates in bilayers might be composed of a bundle of peptides in helical conformation. Besides, similar conductance measurements performed with the whole PP3 protein did not induce any channel fluctuations. However, with the latter, an early breakdown of the bilayers occurred, a finding that can be tentatively explained by a massive incorporation of PP3. In the light of the present results, it could be inferred that PP3 membrane attachment may be achieved by oligomerization of the C-terminal amphipathic helical region.

Regulation of glycosylation-dependent cell adhesion molecule 1 (GlyCAM-1) gene in the mouse mammary gland differs from that of casein genes

Mouse glycosylation-dependent cell adhesion molecule 1 (GlyCAM-1), also known as mC26 and homologous to bovine PP3, is a milk protein synthesized in the mammary gland. Several studies have investigated the regulation of casein, the major milk protein, gene in the mammary gland, but little is known about GlyCAM-1. Here we examined GlyCAM-1 gene expression in mouse mammary epithelial cells. First, we detected GlyCAM-1 expression in mammary epithelial cells in situ by immunohistochemistry; almost all mammary epithelial cells of the lactating mouse expressed GlyCAM-1. Second, mammary epithelial cells were digested with collagenase and cultured with insulin, prolactin and/or glucocorticoid. alpha-Casein and beta-casein genes were expressed following treatment with insulin, prolactin and glucocorticoid. In contrast, GlyCAM-1 expression could not be detected with any combination of these three hormones. We also analyzed changes in the levels of GlyCAM-1 and caseins mRNAs in cultured cells. The addition of hormones to the culture medium increased casein mRNAs, but surprisingly reduced GlyCAM-1 mRNA. Our results suggest that the mechanisms that regulate GlyCAM-1 gene in mammary cells of lactating mice are different from those involved in the regulation of casein genes.

Camel (camelus dromedarius) milk PP3: evidence for an insertion in the amino-terminal sequence of the camel milk whey protein

The camel (camelus dromedarius) milk proteose peptone 3 (PP3) was purified successively by size exclusion fast protein liquid chromatography and reversed phase high performance liquid chromatography and then characterized by amino acid residue composition determination and chemical microsequencing after CNBr or trypsin cleavages. In comparison with the previously reported structure of camel milk whey protein, the camel PP3 contains an insertion in the N-terminal region which has approximately 24 residues, whereas the remaining C-terminal regions of these two homologous proteins are essentially identical. The camel PP3 seems to contain a potential O-glycosylation site localized in this insertion and 2 or 3 phosphorylated serine residues. PP3 belongs to the glycosylation-dependent cell adhesion molecule 1 (GlyCAM-1) family and could therefore play an immunological role in the camel or its suckling young.

A review and proposed nomenclature for major proteins of the milk-fat globule membrane

The characteristics and possible functions of the most abundant proteins associated with the bovine milk-fat globule membrane are reviewed. Under the auspices of the Milk Protein Nomenclature Committee of the ADSA, a revised nomenclature for the major membrane proteins is proposed and discussed in relation to earlier schemes. We recommend that proteins be assigned specific names as they are identified by molecular cloning and sequencing techniques. The practice of identifying proteins according to their Mr, electrophoretic mobility, or staining characteristics should be discontinued, except for uncharacterized proteins. The properties and amino acid sequences of the following proteins are discussed in detail: MUC1, xanthine dehydrogenase/oxidase, CD36, butyrophilin, adipophilin, periodic acid Schiff 6/7 (PAS 6/7), and fatty acid binding protein. In addition, a compilation of less abundant proteins associated with the bovine milk-fat globule membrane is presented.

The structure of the membrane-binding 38 C-terminal residues from bovine PP3 determined by liquid- and solid-state NMR spectroscopy

The secondary structure and membrane-associated conformation of a synthetic peptide corresponding to the putative membrane-binding C-terminal 38 residues of the bovine milk component PP3 was determined using 1H NMR in methanol, CD in methanol and SDS micelles, and 15N solid-state NMR in planar phospholipid bilayers. The solution NMR and CD spectra reveal that the PP3 peptide in methanol and SDS predominantly adopts an alpha-helical conformation extending over its entire length with a potential bend around residue 19. 15N solid-state NMR of two PP3 peptides 15N-labelled at the Gly7 and Ala32 positions, respectively, and dissolved in dimyristoylphosphatidylcholine/dimyristoylphosphatidylglycerol phospholipid bilayers shows that the peptide is associated to the membrane surface with the amphipathic helix axis oriented parallel to the bilayer surface.

Alternative splicing of lactophorin mRNA from lactating mammary gland of the camel (Camelus dromedarius)

The objective of this study was to determine the corrected structure of lactophorin, a major whey protein in camel milk. The protein had 60.4% amino acid sequence identity to a proteose peptone component 3 protein from bovine whey and 30.3% identity to the glycosylation-dependent cell adhesion molecule 1 in mice. The N-terminal heterogeneity of the protein was a result of alternative mRNA splicing. About 75% of the protein was expressed as a long variant A with 137 amino acid residues and a molecular mass of 15.7 kDa; about 25% was as a short variant B with 122 amino acid residues and a molecular mass of 13.8 kDa. Both proteins are probably threefold phosphorylated. In contrast to the related proteins, no glycosylation was found in camel lactophorin. Because of this difference, specific interaction with carbohydrate binding proteins, as reported for the murine protein, can be excluded, and a function of the protein other than cell recognition or rotaviral inhibition is proposed. The concentration of lactophorin in camel milk was found to be about three times higher than the concentration of the bovine homologue in bovine milk. Pronounced similarities existed between the primary and secondary structures of bovine and camel proteins. We speculated that camel lactophorin has a similar function to that of bovine protein in milk, which is supposed to be the prevention of fat globule aggregation and the inhibition of spontaneous lipolysis by lipoprotein lipase.

Identification and characterization of glycosylation-dependent cell adhesion molecule 1-like protein expression in the ovine uterus

Glycosylation-dependent cell adhesion molecule 1 (GlyCAM-1) is an endothelial glycoprotein secreted in lymph nodes that serves as a ligand for leukocyte cell surface selectin and mediates lymphocyte extravasation. In the present studies, rabbit anti-rat GlyCAM-1 IgG was used in immunochemical analyses of GlyCAM-1-like protein in the ovine uterus. In cyclic ewes, GlyCAM-1 expression increased in the endometrial luminal epithelium (LE) and shallow glandular epithelium (cGE) between Days 1 and 5 and then decreased between Days 11 and 15. In pregnant ewes, GlyCAM-1 in the LE and cGE was low on Days 11 and 13, increased on Day 15, and was abundant on Days 17 and 19. Immunoreactive GlyCAM-1 was also detected in the conceptus trophectoderm on Days 13-19. Staining for GlyCAM-1 in the smooth muscle of the vasculature and myometrium was constitutive, and no staining was detected in the stroma. An immunoreactive protein of approximately 45 kDa was identified in endometrial extracts and uterine flushings from cyclic and pregnant ewes. In pregnant ewes, the relative amount of immunoreactive GlyCAM-1 in uterine flushings was low on Days 11 and 13 but high on Days 15 and 17. Results suggest that a GlyCAM-1-like protein may be a secretory product of the endometrial epithelium and/or conceptus trophectoderm. Patterns of distribution observed for immunoreactive GlyCAM-1-like protein in the endometrial epithelium, combined with proposed functions for lymphoid GlyCAM-1, suggest that this mucin glycoprotein may be involved in conceptus-maternal interactions during the periimplantation period of pregnancy in sheep.

The primary structure of caprine PP3: amino acid sequence, phosphorylation, and glycosylation of component PP3 from the proteose-peptone fraction of caprine milk

Proteose-peptone component 3 is a phosphorylated glycoprotein that was isolated from the proteose-peptone fraction of caprine milk. By mass spectrometric analysis, amino acid sequencing, and polymerase chain reaction analysis, the primary structure has been determined and has been shown to contain 136 amino acids. Phosphorylations were identified at Ser30 and Ser41. A partial glycosylation was present at Thr16, and a N-linked glycosylation was present at Asn78. Galactosamine was the amino sugar detected at Thr16. Glucosamine and galactosamine were the amino sugars found in the carbohydrate group linked to Asn78. The caprine amino acid sequence exhibits 88% identity with the bovine proteose-peptone component 3 sequence. However, when compared with the bovine sequence, the caprine sequence contains an insertion of a serine residue at position 25.