Biomedical subjects

Peter Friedrich

Publications and source records attributed to Peter Friedrich.

22 records · Page 2Linked to original sources

PubMed2003

Revisiting ubiquity and tissue specificity of human calpains.

The abundance of mRNAs transcribed from human genes of the calpain superfamily was studied in 72 human tissues and cell types by the Human Multiple Tissue Expression (MTE) Array technique. The analysis included the large subunits of mu- and m-calpains, the small subunits, calpastatin and calpain 3 (p94). Besides specific data on transcriptional activity, two major conclusions emerged: (i) 'ubiquitous' calpains are not expressed in all cell types, and (ii) a 'tissue-specific' calpain may be expressed in many cell types apart from the one in which it is particularly abundant. Therefore, the categoric classification of 'ubiquitous' vs. 'tissue-specific' calpains is a simplification.

Calcium-Binding Proteins↗

PubMed2002

A novel human small subunit of calpains.

Typical calpains are heterodimeric cysteine proteases which have distinct large catalytic subunits (80 kDa) but share a common small regulatory subunit (30 kDa; css1). Here we report the identification, cloning and characterization of a novel human small subunit (css2) encoded by an intronless gene, capns2, located on chromosome 16. This new protein displays 73% sequence identity within the Ca(2+)-binding region but lacks two oligo-Gly stretches characteristic of the N-terminal domain of the conventional small subunit. css2 appears to be the functional equivalent of the conventional small subunit in vitro in that it helps the large subunit fold into the active conformation of similar Ca(2+) sensitivity when the two proteins are co-expressed in Escherichia coli. The purification of various chimaeric rat 80 kDa-human css2 constructs, on the other hand, shows that css2 binds the large subunit much more weakly than css1. Further, it does not undergo the autolytic conversion typical of the classical small subunit. The expression of this protein in vivo, as assessed from its appearance in expressed sequence tag clones, is rather limited, making it an example of a tissue-specific, rather than ubiquitous, small subunit.

Amino Acid Sequence↗

PubMed2002

Calpastatin subdomains A and C are activators of calpain.

The inhibitory domains of calpastatin contain three highly conserved regions, A, B, and C, of which A and C bind calpain in a strictly Ca(2+)-dependent manner but have no inhibitory activity whereas region B inhibits calpain on its own. We synthesized the 19-mer oligopeptides corresponding to regions A and C of human calpastatin domain I and tested their effect on human erythrocyte mu-calpain and rat m-calpain. The two peptides significantly activate both calpains: the Ca(2+) concentration required for half-maximal activity is lowered from 4.3 to 2.4 microm for mu-calpain and from 250 to 140 microm for m-calpain. The EC(50) concentration of the peptides is 7.5 microm for mu-calpain and 25 microm for m-calpain. It is noteworthy that at low Ca(2+) concentrations (1-2 microm for mu-calpain and 70-110 microm for m-calpain) both enzymes are activated about 10-fold by the peptides. Based on these findings, it is suggested that calpastatin fragments may have a role in calpain activation in vivo. Furthermore, these activators open new avenues to cell biological studies of calpain function and eventually may alleviate pathological states caused by calpain malfunction.

Amino Acid Sequence↗

PubMed2002

The role of dimerization in prion replication.

The central theme in prion diseases is the conformational transition of a cellular protein from a physiologic to a pathologic (so-called scrapie) state. Currently, two alternative models exist for the mechanism of this autocatalytic process; in the template assistance model the prion is assumed to be a monomer of the scrapie conformer, whereas in the nucleated polymerization model it is thought to be an amyloid rod. A recent variation on the latter assumes disulfide reshuffling as the mechanism of polymerization. The existence of stable dimers, let alone their mechanistic role, is not taken into account in either of these models. In this paper we review evidence supporting that the dimerization of either the normal or the scrapie state, or both, has a decisive role in prion replication. The contribution of redox changes, i.e., the temporary opening and possible rearrangement of the intramolecular disulfide bridge is also considered. We present a model including these features largely ignored so far and show that it adheres satisfactorily to the observed phenomenology of prion replication.

Animals↗