An insight into molecular mechanism of endocytosis

Endocytosis involving pinocytosis, phagocytosis and receptor-mediated pathway is a central process involved in numerous cellular events: receptor recycling, nutrient uptake, transcytosis, antigen processing and presentation, pathogen uptake etc. Traditionally, the process has been studied using uptake kinetics and immunocytochemistry. In last few decades, additional tools, like mutant analysis, density shift, semi-intact and cell-free systems and electromagnetic separation have helped us to obtain molecular insight into many of the steps involved in endocytosis. New chemical entities, like clathrin and coatomer proteins involved in internalization have been fully characterized. Biomolecules involved in vesicle budding and fusion reactions, like ARF (ADP ribosylation factors), COPs (coat proteins), and SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) have been identified and characterized. Compartment specific molecules, like Rab have also added to our understanding of complex process of endocytosis. Collectively these have led us to an era of molecular endocytosis. The present review gives an overview of the process and describes some of the molecular events of the endocytic process. It also describes methods and approaches used in deciphering the events at cellular and molecular levels.