Calculating the maximum capacity of intracellular transport vesicles

Abstract

In eukaryotic cells, vesicles transport protein cargo to various destinations in the cell. As part of an effort to count the number of cargo molecules in vesicles in cells, we asked a simple question: what is the maximum number of cargo molecules that can be packed into a vesicle? The answer to this question lies in the Tammes Problem, which seeks to determine the packing of circles on a spherical surface. The solution to this problem depends on the sizes of the vesicle and the cargo. We present here the computational results that determine the maximum theoretical capacity of a range of biologically relevant cargo in a variety of meaningful vesicle sizes. Our results could be generalized in order to describe an equation that allows the calculation of the approximate maximum capacity of any vesicle, whatever the size; provided that the size and geometry of the cargo is known. vesicle transport | spherical packing | Tammes Problem | cargo proteins | clathrin-coated vesicleCorrespondence: E.Martins-Ratamero.1@warwick.ac.uk s.j.royle@warwick.ac.uk

Tumor protein D54 defines a new class of intracellular transport vesicles

“…While being small has its advantages, a major disadvantage is that the capacity of INVs is restricted. Small vesicles can actually carry a surprising amount of cargo (Takamori et al, 2006;Martins Ratamero and Royle, 2019 Preprint), but they are presumably restricted for the carriage of large cargo: i.e., those with bulky extracellular domains or large ligands (Martins Ratamero and Royle, 2019 Preprint), although not necessarily (McCaughey et al, 2019). Other classes of vesicle exhibit size adaptability.…”

Intracellular nanovesicles mediate integrin trafficking during cell migration

“…For integrin α IIb β 3, this conformation extends 11 nm (Ye et al, 2008), which indicates that traffic in INVs is possible. Despite their small size, the maximum capacity of an INV is surprisingly high (Martins Ratamero and Royle, 2019), although for bulky cargoes such as integrins, the number traveling in each INV is likely to be low.…”

Remodelling of membrane tubules by the actin cytoskeleton

“…Their formation follows the time sequence previously described, which ends with the release of a transport vesicle that will be carried through the cell. Such transporters gather proteins and lipids needed for the targeted region and vary in composition, size and shape (Ratamero and Royle, 2019). Most transporters are spherical but some can have a tubular shape (Martınez-Menarguez, 2013).…”