**16. Signalling dysfunction**

Dysfunction of cell signalling can have catastrophic consequences. This is certainly one of the main reasons why the topic needs to be more fully understood. Dysfunction can lead to either the lack of functionality or indeed too much activity, with either situation being undesirable. If insulin signalling is taken as an example, a dysfunction of the insulin receptor would mean that the arrival of insulin at the cell surface would not be recognised and no insulin response by the cell would be mounted. Obvious effects of such a dysfunction are conditions such as diabetes. One the other hand, if the G protein Ras is taken as an example, mutation of the coding for amino acids at position 12, 13, or 61 in the sequence leads to a protein which has impaired GTPase activity and therefore can not be turned off (Figure 8). This leads to the signalling pathways in which RAS is involved being in the permanently active state, regardless of the lack of continued initiation of the signalling pathway. *RAS* mutations are found in about one third of human malignancies (Riely *et al.*, 2009). These are just two examples and there are many more, highlighting the importance and impact of correct cell signalling.

Fig. 8. G protein dysfunction can lead to continuous signalling. G proteins can be thought of as being molecular switches, with an "on" and an "off" state. In the inactive state they are bound to GDP, but on activation this is exchanged for GTP, so leading to a conformational change in the protein which allows it to signal (A). The GTP bound form of the G protein will then signal downstream to the next effector in the chain. In the case of the G protein Ras, the next signalling component in the transduction pathway could be the protein kinase Raf. To then inactivate the G protein its intrinsic GTPase activity will convert the GTP back to GDP and inactive the protein – through a reversal of the conformation change. However, in proteins such as Ras, a mutation can disrupt the GTPase active site so stopping the conversion of GTP back to GDP (B). In this case, the protein will continue to be bound to GTP, and continue to be in the conformation that signals. Therefore, even if all the upstream signalling is reversed or halted, the G protein will continue to signal downstream regardless. Because Ras is often on pathways which are invoked by growth factors, continuous G protein signalling can lead to a continuous "grow" signal, and hence lead to tumour growth and cancer.

Dysfunction can and does happen in music too. The discussion above emphasises the fact that many cell signalling events will be taking place in the cell at the same time. There may be many effects, often in different parts of the cell. However, there should be minimal interference of one pathway over the other if they are controlling completely independent effects. At many music venues in recent times there may be several events taking place all at the same time, and the Glastonbury Festival is a good example. People need to listen to the band of their choice without hearing the others in such a way that it disrupts their enjoyment. However, if one band starts to dominate, or the equipment on one band loses its volume, then the effect that the festival envisaged will be compromised, just as the overall signalling network of the cell would be compromised. An example of this would be signals moving into a cell through the gap junctions. The signalling of one cell may overwhelm the signalling in one of its neighbours if second messengers move on mass through the gap junctions. Clearly there needs to be control of such movement and gap junction function and regulation is clearly important to understand (Evans and Martin, 2002).

Although it is less common now physical recordings can cause problems with both vinyl records and CDs able to "jump". This can render the music so bad that it can't be listened too. Other equipment can fail too, including digital instruments and amplifiers. But even more classical equipment can have problems. A sonata played on a piano with a broken key or hammer may make the music very poor. It may not stop the piece being played altogether, and the musician may be able to continue. However, the concert is unlikely to get good reviews and both the musician and venue may struggle to have a future event. Just like in a cell, a small dysfunction may render the longer term future to be in doubt.

### **17. Future and evolution**

64 Biomedical Science, Engineering and Technology

either the lack of functionality or indeed too much activity, with either situation being undesirable. If insulin signalling is taken as an example, a dysfunction of the insulin receptor would mean that the arrival of insulin at the cell surface would not be recognised and no insulin response by the cell would be mounted. Obvious effects of such a dysfunction are conditions such as diabetes. One the other hand, if the G protein Ras is taken as an example, mutation of the coding for amino acids at position 12, 13, or 61 in the sequence leads to a protein which has impaired GTPase activity and therefore can not be turned off (Figure 8). This leads to the signalling pathways in which RAS is involved being in the permanently active state, regardless of the lack of continued initiation of the signalling pathway. *RAS* mutations are found in about one third of human malignancies (Riely *et al.*, 2009). These are just two examples and there are many more, highlighting the

Fig. 8. G protein dysfunction can lead to continuous signalling. G proteins can be thought of as being molecular switches, with an "on" and an "off" state. In the inactive state they are bound to GDP, but on activation this is exchanged for GTP, so leading to a conformational change in the protein which allows it to signal (A). The GTP bound form of the G protein will then signal downstream to the next effector in the chain. In the case of the G protein Ras, the next signalling component in the transduction pathway could be the protein kinase Raf. To then inactivate the G protein its intrinsic GTPase activity will convert the GTP back to GDP and inactive the protein – through a reversal of the conformation change. However, in proteins such as Ras, a mutation can disrupt the GTPase active site so stopping the conversion of GTP back to GDP (B). In this case, the protein will continue to be bound to GTP, and continue to be in the conformation that signals. Therefore, even if all the upstream signalling is reversed or halted, the G protein will continue to signal downstream regardless. Because Ras is often on pathways which are invoked by growth factors, continuous G protein signalling can lead to a continuous "grow" signal, and hence lead to

importance and impact of correct cell signalling.

tumour growth and cancer.

It would be naïve to think that cell signalling has evolved to the point where it will evolve no further. Organisms continue to evolve and the proteins involved in cell signalling will no doubt evolve too, and certainly will not stay the same for eternity. Likewise it would be foolish to think the same about music and instruments.

Over billions of years since life began, cell signalling proteins have mutated and changed to give the polypeptides that we can find today. Since the creation of the first cells some form of signalling was required, both to sense the environment of the cell and to coordinate adaption as the world changed. From an oxygen free atmosphere to the present climate of Earth cells and their signalling have had to adapt along the way. They will continue to change, adapt and no doubt the proteins involved in signalling will increase in number in the future. Perhaps an example of such a change can be seen with the enzyme nitric oxide synthase (NOS). Very recently a NOS has been characterised from a very primitive green algae *Ostreococcus tauri* (Foresi *et al*., 2010). Perhaps this photosynthetic organism inherited its gene for this enzyme from a more primitive cell, one which gave rise to both plants and animals. This is likely as the *O. tauri* amino acid sequence is 45% similar to that of a human gene for NOS. Therefore, the human gene has changed considerably compared to the *O. tauri* gene over time*.* Perhaps more striking is the fact that although *O. tauri* is a primitive plant, higher plants do not seem to have a form of this NOS gene at all. Either it has been lost altogether, or it has been mutated to a form which has yet to be identified. Either way, evolution has been hard at work on this gene, and will no doubt continue such work into the future.

Mutation and duplication of gene can lead to families of proteins. Certainly in signalling families of protein isoforms can be recognised, some with added domains, some with extra phosphorylation sites and some in truncated form. Good examples are phosphatase proteins that remove the phosphate groups from proteins (Cohen *et al.,* 1990).

Musical instruments also evolve, and in many ways in a similar manner to proteins. Some have certainly been around for a long time, but even those that form part of current orchestrates are different from those used by great composers such as Mozart. Furthermore he would never have imagined the possibility of an electric violin, but today his music is often played on such an instrument. Music itself evolves, with successive composers building on the work of those who went before them.

Instruments have changed over the years in a way that resembles that of proteins. Protein isoforms can be created when a gene is copied so there are two versions, and then those genes mutate after a period of time to two separate genes which are able to be characterised, and they would give rise to different but related proteins. Musical instruments are the same. A violin is like a copy of a viola, except one is bigger and plays different notes. Copy it again and make it bigger still and a cello is created, and so on so there is a family of instruments which are recognisable as being related, and yet they have different roles. They could be thought of as isoforms perhaps, just like proteins. Using the piano as an example and again one can see "isoforms" which are all recognisable as pianos, that is the concert grand, the baby grand, the upright, the studio piano and so on. Over the years the piano has been adapted to the place it needs to be placed and the audience it is aimed at. There have formats which are no longer seen, like genes which have disappeared during evolution, and there are new versions being developed and used. There now seems to be a vast array of electric pianos and electronic keyboards, with the idea of using a piano keyboard layout being copied and mutated to develop new instruments.

Music and the instruments used to create it will continue to develop and evolve, just as the proteins which are involved in cell signalling. Especially in the advance of climate change, organisms will need to adapt and it will be cell signalling which coordinates such changes, but the signalling pathways will change too. The future will see the development of new cellular components, and no doubt new musical instruments, especially as new digital technologies are adopted. Not all changes will be beneficial, with mutations in genes no only allowing the future evolution of species but creating dysfunctional proteins along the way causing disease in individuals. No doubt not all new music innovations will be successful either, and the future will be littered with new proteins and musical instruments abandoned by nature and the music industry respectively.
