Cathelicidin LL-37 is one of the few human bactericidal peptides with potent antistaphylococcal activity. In this study we examined the susceptibility of LL-37 to proteolytic degradation by two major proteinases produced by Staphylococcus aureus, a metalloproteinase (aureolysin) and a glutamylendopeptidase (V8 protease). We found that aureolysin cleaved and inactivated LL-37 in a time-and concentration-dependent manner. Analysis of the generated fragments by mass spectroscopy revealed that the initial cleavage of LL-37 by aureolysin occurred between the Arg19-Ile20, Arg23-Ile24, and Leu31-Val32 peptide bonds, instantly annihilating the antibacterial activity of LL-37. In contrast, the V8 proteinase hydrolyzed efficiently only the Glu16-Phe17 peptide bond, rendering the C-terminal fragment refractory to further degradation. This fragment (termed LL-17-37) displayed antibacterial activity against S. aureus at a molar level similar to that of the full-length LL-37 peptide, indicating that the antibacterial activity of LL-37 resides in the C-terminal region. In keeping with LL-37 degradation by aureolysin, S. aureus strains that produce significant amounts of this metalloprotease were found to be less susceptible to LL-17-37 than strains expressing no aureolysin activity. Taken together, these data suggest that aureolysin production by S. aureus contributes to the resistance of this pathogen to the innate immune system of humans mediated by LL-37.

The Alzhlmer Af3 amyloid peptide (A3) is the principal protelnaceous component of amylold associated with Alzheimer disease (AD Since slight differences in structure may affect amyloidogenesis, a thorough knowledge of the actual AP composition of amyloid is therefore important. Moreover, knowledge of the exact structure is important for characterization of the proteolytic enzymes involved in AB formation. In addition, amyloid associated with normal aging has, to our knowledge, not been characterized biochemically and its peptide composition is unknown.In the present work, AP was purified from the cerebral cortex of a number of sporadic AD cases and nondemented elderly controls, as well as two familial AD (FAD) cases. One of the two FAD cases had the APP K670N/M671L mutation (13), and the other had the APP V717I mutation (14). Primary structures and relative abundances of the purified AB variants were determined by N-terminal microsequencing and electrospray-ionization mass spectrometry (ESI-MS).Alzheimer disease (AD) is associated with deposition of amyloid in the brain parenchyma and within the cerebromeningeal vasculature (for review, see ref. 1). Amyloid displaying properties similar to those of AD amyloid can also be detected in normal aging (2). Whether this amyloid accompanies normal aging or is an early histopathological sign of presymptomatic AD is not known. The AD-associated amyloid deposits are mainly composed of the 4-kDa Alzheimer A, amyloid peptide (AB) (3, 4). AB is a proteolytic fragment of a transmembrane glycoprotein, the Alzheimer AP amyloid precursor protein (APP) (5).Since the initial isolation of AP from amyloid deposits (3), a variety of methods for purification and analysis of the peptide have been used (4, 6-8). Various forms of the native peptide have been reported. For instance, it has been stated that the N terminus of AP is blocked (6), that AB is deposited as a mixture of N-terminally truncated ("ragged") variants (4), and that the C terminus is different in vascular and parenchymal AP (7). More recently, it was proposed that A/-(1-40) is the major variant in brain (9) and that cerebrovascular amyloid is composed primarily of A(-(1-40) and Af-(1-42) (10) (Fig. 1)

No abstract