Peptide Antibiotics and Defensins Amino Acids

peptide antibiotics
Other humoral effectors and humoral factors have the ability to lyse microorganisms directly. The best studied of these are a class of small peptide antibiotics known as defensins, which in their active forms are all roughly 30 amino acids long (3,5 kilodaltons), positively charged, and protease-resistant. Each also has three internal disulfide bonds. They are classified as either α or β defensins based on the arrangement of the disulfides, but both classes have nearly the same compact, folded structure consisting of three strands of antiparallel β-pleated sheets. (more…)

Antimicrobial Enzymes and Binding Proteins

antimicrobial enzymes
A few of the best known humoral effectors of innate immunity are listed in Table 1 bellow, along with the types of target molecules they recognize. Some are enzymes that can directly injure or kill microbial pathogens. An example is lysozyme, an endoglycosidase found in human saliva, mucus, tears, and other secretions, which attacks the protective cell wall encasing every bacterial cell. Lysozyme acts by digesting the peptidoglycan meshwork formed by long carbohydrate chains of alternating N-acetylmuramic acid and N-acetylglucosamine residues, crosslinked covalently by short oligopeptide sidechains which is a major constituent of all bacterial cell walls but is not found in mammalian tissues. (more…)

Humoral Immune System and Innate Immunity

humoral immune system
The body’s innate resistance to many pathogens is provided by enzymes and other proteins in the blood and tissue fluids. These proteins are the effectors (ie, the active agents) of humoral innate immunity, and they have features in common with one another that are also characteristics of the innate immune system as a whole. First, these proteins are continually expressed throughout life, regardless of whether or not their protective effects are needed at a given moment. Second, although many of these proteins can be produced in higher quantities in times of need, their intrinsic properties (eg, substrate specificity and ige binding affinity) never change: The characteristics of these proteins have been shaped by evolution, are genetically determined, and are fixed at birth, so that they do not vary during an individual’s lifetime. (more…)