Role of the HIV-1 envelope transmembrane domain in intracellular sorting

Role of key amino acids in the transmembrane domain of the Newcastle disease virus fusion protein

Newcastle disease (ND), caused by the Newcastle disease virus (NDV), is transmitted by poultry with severe infectivity and a high fatality rate. The fusion (F) protein on the NDV envelope facilitates the merger of the viral and host cell membranes with the help of the homologous hemagglutinin-neuraminidase protein (HN). The transmembrane (TM) domains of viral fusion proteins are typically required for fusion, but the key amino acids in NDV F TM domains have not been identified. Site-directed mutagenesis was utilized to change the conserved amino acids at 500, 501, 502, 505, 510, 513, 516, 519, and 520 to alanine. It was found that mutants L519 and V520 had an interrupted protein expression, decreased to below 10%, and mutants A500, I505, V513, and V516 had a hypoactive impact on fusion activity, decreased to 85.38%, 67.05%, 55.38% and 51.13% of wt F, respectively. The results indicated that the TM domain plays a vital part in the fusion activity of the NDV F protein.

Viral Membrane Fusion and the Transmembrane Domain

Initiation of host cell infection by an enveloped virus requires a viral-to-host cell membrane fusion event. This event is mediated by at least one viral transmembrane glycoprotein, termed the fusion protein, which is a key therapeutic target. Viral fusion proteins have been studied for decades, and numerous critical insights into their function have been elucidated. However, the transmembrane region remains one of the most poorly understood facets of these proteins. In the past ten years, the field has made significant advances in understanding the role of the membrane-spanning region of viral fusion proteins. We summarize developments made in the past decade that have contributed to the understanding of the transmembrane region of viral fusion proteins, highlighting not only their critical role in the membrane fusion process, but further demonstrating their involvement in several aspects of the viral lifecycle.

Identification of the endoplasmic reticulum localization sequence and N-glycosylation of matrix metalloproteinase 26

Matrix metalloproteinase 26 (MMP-26), also called endometase and matrilysin-2, belongs to the MMP superfamily. Previous studies have focused on its role in tumor invasion and migration but detailed subcellular localization of MMP-26 remains poorly understood. In this study, sequence deletion mutants of MMP-26 revealed that residues 88-123 function to localize MMP-26 to the endoplasmic reticulum (ER). Moreover, using homologous recombination, we show that exchanging residues 88-123 of secretory MMP-7 with the same region in MMP-26 causes localization of this MMP-7 construct to the ER. Moreover, two (N64, N221) of the three possible N-glycosylation sites in MMP-26 were shown to be N-glycosylated, and N-glycosylation is not required for ER localization. These results demonstrate that the 88-123 region of MMP-26 is a noncanonical ER retention signal and MMP-26 is an N-glycosylated protein, thereby providing novel insights into the properties of MMP-26 within the cell.