Carbonylation of proteins-an element of plant ageing

Abstract

Carbonylation-ROS-dependent posttranslational modification of proteins-may be regarded as one of the important events in the process of ageing or senescence in plants. Ageing is the progressive process starting from seed development (plants) and birth (animals). The life-span of living organisms depends on many factors and stresses, which influence reactive oxygen species (ROS) level. The imbalance of their production and scavenging causes pathophysiological conditions that accelerate ageing. ROS modify nucleic acids, lipids, sugars and proteins. The level of carbonylated proteins can serve as an indicator of an oxidative cellular status. Several pathways of protein carbonylation, e.g. the conjugation with reactive carbonyl species, and/or a direct metal-catalysed oxidative attack on amino acids residues are known. Dysfunctional carbonylated proteins are more prone to degradation or form aggregates when the proteolytic machinery is inhibited, as observed in ageing. Protein carbonylation may contribute to formation of organelle-specific signal and to the control of protein quality. Carbonylated proteins are formed during the whole plant life; nevertheless, accelerated ageing stimulates the accumulation of carbonyl derivatives. In the medicine-related literature, concerned ageing and ROS-mediated protein modifications, this topic is extensively analysed, in comparison to the plant science. In plant science, ageing and senescence are considered to describe slightly different processes (physiological events). However, senescence (Latin: senēscere) means "to grow old". This review describes the correlation of protein carbonylation level to ageing or/and senescence in plants. Comparing data from the area of plant and animal research, it is assumed that some basic mechanism of time-dependent alterations in the cellular biochemical processes are common and the protein carbonylation is one of the important causes of ageing.

Keywords: Carbonyl groups; Posttranslational protein modification; ROS; Senescence.

Fig. 1

Changes in the level of carbonylated proteins during the life of a tree. a The progression of plant ageing. The highest level of the proteins marked with CO groups is achieved at last part of life-span (internal and external symptoms of tissues senescence). b Seasonal, environmental-dependent changes. Leaf senescence is not linked to ageing of the whole plant organism (the leafless tree) and is accompanied by an increase of carbonylated proteins level. The lowest content of oxidized proteins is achieved before the production of the offspring (the blooming tree)

Fig. 2

The most common pathways of protein carbonylation include direct ROS attack on amino acid residues (Pro, Arg, Lys and Thr), metal-catalysed oxidation (MCO) attack on Lys, Arg, Pro and Thr residues in the presence of ROS and reduced metal ions, adduction of advanced glycation end products (AGEs) formed in the presence of ROS, reduced metal ions and reducing sugars, e.g. glucose (Glu), and incorporation of products of lipid peroxidation, e.g. 4-hydroxynonenal. R represents amino acid residue of targeted protein for carbonylation

Fig. 3

Ageing imprinted into the program of life-span or accelerated by anthropogenic and environmental stress factors is linked to the increase of carbonylated proteins level. The enhanced content of oxidized proteins may negatively implicate proteolytic machinery leading to the formation of proteins aggregates