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Background: An antagonistic anti-PCSK9 antibody exhibits target-mediated clearance, resulting in a dose-dependent PK. Results: Engineering of an antibody with pH-sensitive binding to PCSK9 decreases target-mediated clearance, resulting in increased PK and efficacy in vivo. Conclusion: pH-sensitive anti-PCSK9 antibodies are excellent candidates for therapeutic development. Significance: pH-sensitive antibodies may enable less frequent or lower dosing of antibodies hampered by target-mediated clearance and high antigen load.

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The 0 protein ofbacteriophage X localizes the initiation of DNA replication to a unique site on the A genome, oriX. By means of electron microscopy, we infer that the binding of 0 to oriX initiates a series of protein addition and transfer reactions that culminate in localized unwinding of the origin DNA, generating a prepriming structure for the initiation of DNA replication. We can define three stages to this prepriming reaction, the first two of which we have characterized previously. First, dimeric 0 protein binds to multiple DNA binding sites and self-associates to form a nucleoprotein structure, the O-some. Second, A P and host DnaB proteins interact with the O-some to generate a larger complex that includes additional DNA from an A+T-rich region adjacent to the 0 binding sites. Third, the addition ofthe DnaJ, DnaK, and Ssb proteins and ATP results in an origin-specific unwinding reaction, probably catalyzed by the helicase activity of DnaB. The unwinding reaction is unidirectional, proceeding "rightward" from the origin. The minimal DNA sequence competent for unwinding consists of two 0 binding sites and the adjacent A+T-rich region to the right of the binding sites. We conclude that the A 0 protein localizes and initiates a six-protein sequential reaction responsible for but preceding the precise initiation of DNA replication. Specialized nucleoprotein structures similar to the O-some may be a general feature of DNA transactions requiring extraordinary precision in localization and control.Bacteriophage X initiates DNA replication at a single replication origin, oriX (1-3). The DNA sequence of the oriX region has two major characteristics: four direct repeats of 18 base pairs (bp), each of which is an inverted repeat; and an adjacent region to the right of the repeats that is extremely rich in A+T (4-6). Two X proteins, 0 and P, are required for viral DNA replication (7-9). The 0 protein recognizes the origin, and P localizes the essential replication enzymes of Escherichia coli at this site by initiating a series of protein-protein interactions (3). The 0 protein binds to the four repeats (10, 11), probably recognizing each local inverted repeat as a dimer (ref. 12; unpublished work In this study, we show that the third stage ofthe prepriming reaction yields origin-specific unwinding of duplex DNA, presumably catalyzed by the helicase activity of DnaB (26). We infer that a locally unwound DNA structure associated with DnaB becomes the specific substrate for localized priming by DnaG. Thus, the 0 protein builds a nucleoprotein structure at the replication origin of A and initiates a series of protein assembly events culminating in the localized initiation of DNA replication. The DnaA protein of E. coli appears to act in a similar fashion to localize the initiation of bacterial DNA replication to the single site, oriC (27, 28 (18,30,32,33). Restriction enzymes were from New England Biolabs.DNA. The structure and preparation of plasmid pRLM4, which contains the replication origin of phage X, have ...

A RIP-like protein, RIP3, has recently been reported that contains an N-terminal kinase domain and a novel Cterminal domain that promotes apoptosis. These experiments further characterize RIP3-mediated apoptosis and NF-U UB activation. Northern blots indicate that rip3 mRNA displays a restricted pattern of expression including regions of the adult central nervous system. The rip3 gene was localized by fluorescent in situ hybridization to human chromosome 14q11.2, a region frequently altered in several types of neoplasia. RIP3-mediated apoptosis was inhibited by Bcl-2, Bcl-x L , dominant-negative FADD, as well as the general caspase inhibitor Z-VAD. Further dissection of caspase involvement in RIP3-induced apoptosis indicated inhibition by the more specific inhibitors Z-DEVD (caspase-3, -6, -7, -8, and -10) and Z-VDVAD (caspase-2). However, caspase-1, -6, -8 and -9 inhibitors had little or no effect on RIP3-mediated apoptosis. Mutational analysis of RIP3 revealed that the C-terminus of RIP3 contributed to its apoptotic activity. This region is similar, but distinct, to the death domain found in many pro-apoptotic receptors and adapter proteins, including FAS, FADD, TNFR1, and RIP. Furthermore, point mutations of RIP3 at amino acids conserved among death domains, abrogated its apoptotic activity. RIP3 was localized by immunofluorescence to the mitochondrion and may play a key role in the mitochondrial disruptions often associated with apoptosis.z 2000 Federation of European Biochemical Societies.