ABSTRACT
The human CD21 is a receptor for cleavage fragments of the third complement component and for Epstein-Barr virus. Previous mutational studies showed that the cytoplasmic domain of CD21 is absolutely required for internalization of either ligand. With the exception of CD19, CD81, Leu-13 and CD35 that can form a complex with CD21 at the cell surface, no other partner that interacts with the hCD21 transmembrane or the cytoplasmic domain was identified. We investigated the internalization capacity of hCD21 tail mutants in the absence of B cell receptor cross-linking by using stable murine B cell transfectants. We provide evidence that at least two internalization motifs are activated when hCD21 binds a monoclonal antibody. In order to identify the cellular proteins that interact with the hCD21 transmembrane and cytoplasmic domains, we combined a mutational mapping with a two-hybrid system approach both in yeast and in mammalian cells. We identified four novel partners that are involved in intracellular trafficking, sorting or cytoskeleton remodeling and we mapped the hCD21 transmembrane and tail subdomains they interact with. We discuss the potential physiological significance of these findings in the context of hCD21 internalization and intracellular trafficking.
Subject(s)
Endocytosis , Receptors, Complement 3d/immunology , Amino Acids , Animals , Cell Line , Humans , Mice , Protein Binding , Protein Interaction Mapping , Protein Structure, Tertiary , Receptors, Complement 3d/chemistry , Two-Hybrid System Techniques , YeastsABSTRACT
We previously reported that a 350-bp region of the adeno-associated virus (AAV) type 2 rep gene contains a cis-acting element responsible for the Rep-dependent replication of a transiently transfected rep-cap plasmid. In this study, we further report that replicated rep-cap sequences can be packaged into AAV capsids in the absence of the inverted terminal repeats.
