Structural basis of C-terminal ß-amyloid peptide binding by the antibody ponezumab for the treatment of Alzheimer's disease.

Alzheimer's disease, the most common cause of dementia in the elderly and characterized by the deposition and accumulation of plaques, is composed in part of ß-amyloid (Aß) peptides, loss of neurons, and the accumulation of neurofibrillary tangles. Here, we describe ponezumab, a humanized monoclonal antibody, and show how it binds specifically to the carboxyl (C)-terminus of Aß40. Ponezumab can label Aß that is deposited in brain parenchyma found in sections from Alzheimer's disease casualties and in transgenic mouse models that overexpress Aß. Importantly, ponezumab does not label full-length, non-cleaved amyloid precursor protein on the cell surface. The C-terminal epitope of the soluble Aß present in the circulation appears to be available for ponezumab binding because systemic administration of ponezumab greatly elevates plasma Aß40 levels in a dose-dependent fashion after administration to a mouse model that overexpress human Aß. Administration of ponezumab to transgenic mice also led to a dose-dependent reduction in hippocampal amyloid load. To further explore the nature of ponezumab binding to Aß40, we determined the X-ray crystal structure of ponezumab in complex with Aß40 and found that the Aß40 carboxyl moiety makes extensive contacts with ponezumab. Furthermore, the structure-function analysis supported this critical requirement for carboxy group of AßV40 in the Aß-ponezumab interaction. These findings provide novel structural insights into the in vivo conformation of the C-terminus of Aß40 and the brain Aß-lowering efficacy that we observed following administration of ponezumab in transgenic mouse models.

Structure of the ESCRT-II endosomal trafficking complex.

The multivesicular-body (MVB) pathway delivers transmembrane proteins and lipids to the lumen of the endosome. The multivesicular-body sorting pathway has crucial roles in growth-factor-receptor downregulation, developmental signalling, regulation of the immune response and the budding of certain enveloped viruses such as human immunodeficiency virus. Ubiquitination is a signal for sorting into the MVB pathway, which also requires the functions of three protein complexes, termed ESCRT-I, -II and -III (endosomal sorting complex required for transport). Here we report the crystal structure of the core of the yeast ESCRT-II complex, which contains one molecule of the Vps protein Vps22, the carboxy-terminal domain of Vps36 and two molecules of Vps25, and has the shape of a capital letter 'Y'. The amino-terminal coiled coil of Vps22 and the flexible linker leading to the ubiquitin-binding NZF domain of Vps36 both protrude from the tip of one branch of the 'Y'. Vps22 and Vps36 form nearly equivalent interactions with the two Vps25 molecules at the centre of the 'Y'. The structure suggests how ubiquitinated cargo could be passed between ESCRT components of the MVB pathway through the sequential transfer of ubiquitinated cargo from one complex to the next.