Isolation and determination of the primary structure of a lectin protein from the serum of the American alligator (Alligator mississippiensis)

Identification and characterization of yak α-lactalbumin and β-lactoglobulin

α-Lactalbumin (α-LA) and β-lactoglobulin (β-LG) were isolated from yak milk and identified by mass spectrometry. The variant of α-LA (L8IIC8) in yak milk had 123 amino acids, and the sequence differed from α-LA from bovine milk. The amino acid at site 71 was Asn (N) in domestic yak milk, but Asp (D) in bovine and wild yak milk sequences. Yak β-LG had 2 variants, β-LG A (P02754) and β-LG E (L8J1Z0). Both domestic yak and wild yak milk contained β-LG E, but it was absent in bovine milk. The amino acid at site 158 of β-Lg E was Gly (G) in yak but Glu (E) in bovine. The yak α-LA and β-LG secondary structures were slightly different from those in bovine milk. The denaturation temperatures of yak α-LA and β-LG were 52.1°C and 80.9°C, respectively. This study provides insights relevant to food functionality, food safety control, and the biological properties of yak milk products.

Plasma complement activation mechanisms differ in ornate (Terrapene ornata ornata) and eastern box turtles (Terrapene carolina carolina)

Eastern (Terrapene carolina carolina) and ornate (Terrapene ornata ornata) box turtles have robust plasma antibacterial activity, however, the mechanism behind this activity is unknown. We used sheep red blood cell (SRBC) hemolysis assays, mannan-affinity chromatography, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) to explore the mechanisms of complement activity in box turtles. Plasma from both species demonstrated volume, time, and temperature-dependent SRBC hemolysis, with significantly greater hemolytic activity in ornate box turtle plasma. Hemolytic activity was highly attenuated following treatment with heat, EDTA, and salicylaldoxime in both species, but was unchanged after treatment with methylamine and ammonium hydroxide. Two abundant mannan-binding proteins (presumed C-type lectins) were identified in eastern box turtle plasma using SDS-PAGE and MALDI-TOF, but ornate box turtles did not express either protein. Eastern box turtles appear to rely on the lectin pathway of complement activation while ornate box turtles utilize the alternative pathway. This study provides further evidence that mechanisms underlying immune function are not always conserved between closely related species. This finding may have important implications for explaining species differences in susceptibility to emerging threats such as disease, toxicants, and climate change.

Different mechanisms of serum complement activation in the plasma of common (Chelydra serpentina) and alligator (Macrochelys temminckii) snapping turtles

Reptiles are declining worldwide yet our understanding of their immune function lags far behind other taxa. The innate immune system is the primary mode of defense in reptiles, and the serum complement cascade is its major component. We assessed serum complement activity of plasma in two closely related aquatic turtle species, the common snapping turtle (CST; Chelydra serpentina) and alligator snapping turtle (AST; Macrochelys temminckii). We used a sheep red blood cell (SRBC) hemolysis assay to assess serum complement activity. Although the antibacterial activities of the plasma of these turtle species are similar, the hemolytic activity was much stronger in CST than AST. Treatment with inhibitors of the serum complement cascade indicated differences in the mechanisms of complement activation between the turtle species. We subjected plasma from both turtle species to mannan affinity chromatography and analyzed the eluate with SDS-PAGE, which revealed that plasma from the CSTs contained only small amounts of one C-type lectin protein while the AST plasma contained high concentrations of two C-type lectins (31.0 and 35.9 kDa). Edman degradation analyses confirmed that the two AST proteins contained identical N-terminal sequences. Thus, the CST appears to rely more heavily on the alternative mechanism of serum complement activation, while the AST appears to rely more on the lectin-mediated pathway, which is a pattern recognition response to prokaryotes not activated by the SRBCs. These results are unique in that the use of serum complement pathways are generally assumed to be conserved within clades.

Purification and characterization of a novel lectin from Chinese leek seeds

A novel lectin, CLSL, was purified from Chinese leek seeds by ion exchange chromatography on SP Sephadex C-25 and gel filtration chromatography on Sephadex G50. The lectin had a molecular weight of 23.6 kDa and was composed of two identical subunits linked by disulfide bonds, a conclusion based on SDS-PAGE under reducing and nonreducing conditions. CLSL was a glycoprotein with a carbohydrate content of 3.6%. It exerted potent agglutinating activity against rat red blood cells at a concentration of 8.9 μg/mL. Hemagglutination of rat erythrocytes was inhibited by d-fructose, mannitol, and sorbose at the concentration of 20 mM. The hemagglutinating activity of CLSL was maintained at 100 °C for 60 min and under acidic pH conditions but was lost at neutral and alkaline pH conditions. The hemagglutinating activity was stimulated by Ca(2+), Fe(2+), and Cu(2+) but inactivated by Ba(2+) at a concentration of 10 mM. Ba(2+)-mediated inactivation of CLSL was caused by CLSL conformational change induced by barium ions, according to the results of circular dichroism and fluorescence spectroscopy. Deconvolution of the CLSL circular dichroism indicated that it was an α-helical lectin with α-helix and β-fold contents of 35.8% and 8.6%, respectively. CLSL could also selectively inhibit cell proliferation.

Comparative genomic and phylogenetic analyses of the intelectin gene family: implications for their origin and evolution

Intelectin is a newly characterized gene family involved in early embryogenesis, host-pathogen interactions and iron metabolism. In this study, we searched the genomes of metazoans by extensive BLAST survey and found no intelectin homologs in invertebrate metazoans but 12 in amphioxus Branchiostoma floridae and 21 in ascidians Ciona intestinalis. Some ascidians oocyte cortical granule lectins (CGLs) have unknown insertion sequences between fibrinogen-related domain (FReD) and Intelectin Domain, the boundaries of which are equivalent to exon structures. In addition to ascidians intelectins/CGLs located in the base, phylogenetic tree comprises four main clades representing mammal, frog, fish, and amphioxus, indicating that intelectin genes undergo extensive lineage-specific duplication or gene conversion. However, genomic neighborhood surrounding analysis shows that clear proto-orthologies are difficult to be established among these counterparts. In addition, sequence comparison and phylogenetic analysis of FReDs from intelectins and other fibrinogen-like proteins from choanoflagellate, anemone, frog and human indicate FReDs of intelectins are unique. Likewise, these choanoflagellate and anemone genes may be close to intelectin gene.