No abstract

Human papain-like cathepsins were long believed to be responsible for terminal protein degradation in the lysosomes. This view changed dramatically when they were found to be involved in a number of important cellular processes, such as antigen presentation [7]. Their high proteolytic potential, which can be very harmful, requires the activity of papain-like cathepsins to be strictly regulated. Their endogenous protein inhibitors act as one of the main means of regulation [8]. The best characterized are the cystatins, which comprise a superfamily of evolutionarily related proteins, each consisting of at least one domain of 100-120 amino acid residues with conserved sequence motifs [8][9][10][11]. Type I cystatins (the stefins), stefins A and B, are cytosolic, % 100 amino acid residue-long proteins lacking disulfide bridges. Type II cystatins, cystatins C, D, E ⁄ M, F, S, SA, SN are longer extracellular proteins, consisting of % 120 amino acid residues and containing two disulfide bridges. Type III cystatins, the kininogens, are large multifunctional plasma proteins, containing three type II cystatin-like domains.Cystatin F was discovered recently by three independent groups. Two of them identified it by cDNA cloning and named the new inhibitor leukocystatin [12]

No abstract

The mechanism by which proteins form amyloid fibrils is of high interest to the scientific community as its understanding could resolve questions relevant to conformational diseases. The structural and energetic basis of the process is still largely unknown. The main controversial issue is the co-existence of several protein conformations. Three models for the mechanism of protein fibrillogenesis have been proposed which need to be tested by experiments. In this report, amyloid fibrils grown from human stefin B (type I cystatin) are described. This physiologically relevant protein readily forms fibrils in vitro, in contrast to the homologue--human stefin A--which forms fibrils under extreme conditions only. In order to specifically label stefin B fibrils in vitro, rabbit polyclonal antibody and mouse monoclonal antibody A6/2 against human stefin B were used for immunogold labelling. Samples were examined by transmission electron microscopy. Fibrils of stefin B were strongly labelled using polyclonal antibody and Protein A gold, whereas no positive reaction was observed with monoclonal antibody A6/2.

SUMMARYActivation of the CD4 + T-cell mediated immune response relies on the proteolytic capacity of enzymes involved in modulating major histocompatibility complex (MHC) II-associated antigen presentation in antigen-presenting cells (APC). The MHC II-associated chaperone molecule p41 isoform of invariant chain (inhibitory p41 Ii) has been suggested to regulate stability and activity of cathepsin L in these APC. In the present study the human lymph node distribution of noninhibitory p31 Ii and inhibitory p41 Ii have been compared by differential labelling, using two specific monoclonal antibodies. The distribution of p41 Ii, but not p31 Ii, matched the distribution of cathepsins L and H in subcapsular and cortical sinuses and germinal centres. Co-localization of p41 Ii with cathepsin H was confirmed in strongly CD68 + sinus-lining macrophages, acting as APC. Furthermore, p41 Ii was determined together with cathepsins L and H in tingible body macrophages, highly phagocytic, but not antigen-presenting cells inside germinal centres. With respect to the physiological function that these two populations of macrophages have in human lymph nodes, our results support a regulatory function of p41 Ii towards cathepsins L and H in human macrophages, associated with the processes of phagocytosis rather than antigen presentation.