Protein homeostasis refers to the ability of cells in the body to properly manufacture, fold, and deactivate protein molecules, so that the body can respond to external challenges and changes in internal conditions. Constructed out of chains of amino acids, proteins rely on the correct folding sequence to form three-dimensional structures capable of performing their intended functions. Disruptions to this homeostasis can lead to proteins that are abnormally folded, which can change the way they operate, and, in some cases, even induce disease states.
Genes have a major influence over the maintenance of protein homeostasis. Expressing genes, or allowing them to interact with other components of the cell to form proteins, is one way that this is accomplished. Another is through the creation of special proteins, called folding enzymes, whose shapes and actions help guide the formation of newly made proteins into their proper three-dimensional structures. When proteins are no longer needed for particular situations, pathways may lead to the expression of genes that create other enzymes that allow them to be safely disposed of. The component amino acids that make up proteins can then be re-used after this degradation takes place.
Cells must be able to respond to a variety of new conditions, and protein homeostasis plays an important role in this process. Signals from the environment can induce the creation of proteins that allow for cells to manage these novel situations. These signals may be issued from inside of a single cell, a single organ, or even other organs, depending on the extent of the changes that the organism is responding to.
Feedback mechanisms also help to maintain protein homeostasis, and this feedback can also involve multiple organs. Enzymes and cellular structures interact with newly made proteins to ensure that they are folded into their correct conformations. Information on this folding may be sent to the nucleus of the cell, or even to the brain, which can then send back return messages about further actions to take. Irregular proteins, for example, may lead to feedback signals ordering their destruction.
Disease states can arise from disturbing protein homeostasis. Alzheimer's disease, for example, may involve problems with feedback mechanisms that can lead to the overproduction of certain proteins which are improperly folded. Other conditions, such as cystic fibrosis, may have underlying factors that lead to an inability to create certain proteins necessary for healthy functioning. Different aspects of the aging process may involve the progressive disruption of the feedback networks that normally help to maintain homeostasis, as well.