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Cell Vesicles Coats and Irreducible Complexity

Cell Vesicles Coats

Living cells contain vesicles, sacs that transport water and substances like proteins and lipids among different compartments of the cell, including between the endoplasmic reticulum (ER) and the Golgi apparatus, or between the outside and the interior of the cell.

The formation of such trafficking vesicles is among the most fundamental processes taking place in the cell.

A team of scientists of the European Molecular Biology Laboratory (EMBL) at Heidelberg has produced – using low-temperature cryo-electron tomography – the most detailed pictures ever obtained of the coats surrounding transport vesicles, images that have revealed a thus-far unimagined complexity.

This is the first time that a model of a complete assembled vesicle coat has been realised. The study, published in Science earlier this month, contradicts the current “adaptor-and-cage” view of coated vesicle formation.

The way these highly interconnected coats, made of proteins, function has been compared to a self-driving car which, when you walk out of your front door, assembles around you, rises from the ground, takes you to your destination levitating in the air, then disassembles, ready to pick up another passenger. Something very similar does happen in biological cells.

Progress in science constantly shows that life is much more intricated, sophisticated and complex than we suppose.

There are three types of known transport vesicles, each with its specific type of coat which is composed of different proteins and assembles onto a membrane surrounding the vesicle: Clathrin-coated vesicle (CCV), Coat Protein 1 (COPI), Coat Protein 2 (COPII).

While it was believed that the assembled COPI coat was similar to Clathrin and COPII, it was found instead that it is more complicated, having seven proteins coming together simultaneously and forming complexes with triangular symmetry that allow the complex to attach to the vesicle membrane. The “triads” forming the coat are called “coatomers”:

[A]ssembled coatomer can adopt different conformations to interact with different numbers of neighbors. By regulating the relative frequencies of different triad patterns in the COPI coat during assembly — for example, by stabilizing particular coatomer conformations — the cell would have a mechanism to adapt vesicle size and shape to cargoes of different sizes.

Evolution News website comments:

The complexity of these coats, and the accessory proteins that build them, attach them to vesicles and disassemble them, defy unguided evolutionary explanations. They exhibit irreducible complexity; they don’t work unless all the protein parts are present simultaneously.

An irreducibly complex mechanism is such that it cannot work unless all its components are present at the same time.

Many machines exhibit this property. But so do many biological mechanisms and organs.

University of Illinois biologist Tom Frazzetta, in his 1975 classic Complex Adaptations in Evolving Populations (Amazon USA) (Amazon UK) , wrote:

When modifying the design of a machine, an engineer is not bound by the need to maintain a real continuity between the first machine and the next modification .. But in evolution, transitions from one type to the next presumably involve a greater continuity by means of a vast number of intermediate types. Not only must the end product – the final machine – be feasible, but so must be all the intermediates. The evolutionary problem is, in a real sense, the gradual improvement of a machine while it is running.

Frazzetta, an expert in functional biomechanics (the study of how animals work) had for many years studied and dissected the skulls of the bolyerine snakes, rare snakes of the Island of Mauritius. These animals, similar to boas, have a unique anatomical specialisation: their upper jaw is made up of two segments joined together and requiring many specialised tendons, bones, ligaments, muscles, nerves and other tissues.

This characteristic allows the bolyerine snakes to bend the front half of their divided upper jaw backwards when attacking a prey, resulting in a wider opening of the mouth.

How could this system of interconnected tendons, ligaments, muscles, bones and nerves have evolved gradually, as neo-Darwinism contends? It’s an all-or-nothing situation.

No intermediate condition could have worked and consented the viability of this species.

As evolutionist Stephen Jay Gould put it in “The Return of Hopeful Monsters”: “How can a jawbone be half broken?”

These findings have been published in a report titled : “A structure of the COPI coat and the role of coat proteins in membrane vesicle assembly”.

About the author

Enza Ferreri

Enza Ferreri is an Italian-born, London-based Philosophy graduate, writer and journalist. She has been a London correspondent for several Italian magazines and newspapers, including Panorama, L’Espresso, La Repubblica. She blogs at www.enzaferreri.blogspot.co.uk.