Researchers at the Salk Institute for Biological Studies led by Vicki Lundblad, Ph.D., a Professor in the Molecular and Cell Biology Laboratory, have discovered that a protein that helps elongate chromosome ends—and hence saves cells from premature growth arrest—likely recognizes where to report to work through a common fold. Those findings are reported ahead of print in the August 24 online edition of Nature Structure and Molecular Biology.
“Our studies have predicted a specific 3-dimensional shape displayed by a key protein that interacts with telomeres,” said Lundblad, explaining that analysis of this protein, called Est3, had been up to now particularly problematic. “This prediction has now provided us with a crucial tool that has propelled forward our studies of this protein.”
When cells divide, telomeres – the tails of repetitive DNA that extend from the ends of each chromosome – become progressively shorter. Telomeres function like cellular clocks: as they become critically stubby cells are no longer capable of dividing and undergo growth arrest termed cellular “senescence”. Fortunately, over the course of a cell’s lifetime, an enzyme complex known as telomerase works to restore telomeres to a more youthful length after each cell division.
Although the precise structure of human telomerase is not yet known, Lundblad had defined its budding yeast equivalent as containing three Est proteins complexed to an RNA ribbon: Est2 and the RNA do the heavy catalytic lifting in terms of telomere-reconstruction, while Est1 and Est3 orchestrate the process. But just how the two proteins ensured that things run smoothly was still unclear.
An earlier study in Lundblad’s group already answered this question for Est1: they showed that Est drags the telomerase complex to telomeres, an activity that is required to keep yeast cells continuously dividing. “Without Est1, telomerase cannot get to the ends of chromosomes, and thus telomeres shorten,” explained Lundblad.
In the current study Lundblad and co-first authors post-doctoral researcher Jaesung Lee, Ph.D., and graduate student Edward Mandell turned their attention to Est3 by first examining its computer-generated three-dimensional structure. They found that, like several other telomeric proteins, Est3 exhibited an architectural element known as an “OB” fold. Using computer models to scrutinize the fold surface, the group predicted that specific amino acids on one face of the fold might be required for interaction with the telomerase complex.
Laborious benchwork confirmed their predictions: the group biochemically inactivated each candidate amino acid separately, put each of those mutant proteins back into yeast cells, and then monitored whether that manipulation had any effect on telomere length or cell survival.
Their exhaustive analysis proved highly fruitful in terms of telomerase regulation: inactivation of a handful of suspect amino acids on one side of the surface of the protein produced shorter telomeres, showing that telomerase was now severely impaired.
Alterations in one cluster of amino acids lead to failure of Est3 to interact with its other Est protein partners. Disrupting a second set of amino acids leaves the telomerase complex intact, but with an inactive Est3 protein. Addressing what makes Est3 inactive is the subject of ongoing investigation.
“The recent increase in the ability to predict protein structure is now permitting detailed analysis of many proteins, including proteins like Est3, whose function had been mysterious,” says Lundblad.
An unanticipated but highly intriguing finding came from comparison of Est3 structure to that of other proteins. The group found that Est3 highly resembles a mammalian telomere-associated protein called TPP1. “This is surprising because TPP1 is not a subunit of the telomerase complex,” explained Lundblad, noting that instead TPP1’s job is to bind to and shelter telomeres from cellular repair enzymes that might mistake shaggy chromosome ends for damaged DNA — not to regulate their construction.
Factors that regulate telomerase activity are a very hot topic in biomedicine: sluggish telomerase activity promotes premature cell death and may underlie diseases of aging via telomere shortening, while hyperactive telomerase could promote uncontrolled cell division and cellular immortality associated with cancer.
The common architecture of telomere-associated proteins that serve discrete functions is further evidence that shared protein motifs, as exemplified by the signature OB-fold, do not always determine what biochemical task a protein accomplishes but rather signal where it does it.
Or as Lundblad concluded, “What we now propose that this particular protein fold, which both Est3 and TPP1 exhibit, is uniquely suited to the telomere.”
Researchers who also contributed to the study include graduate student Timothy Tucey and Danna Morris, a former graduate student in Lundblad’s lab.
The research was supported by funding from the National Institute on Aging at the NIH.
Salk Institute for Biological Studies in La Jolla, California, is an independent nonprofit organization dedicated to fundamental discoveries in the life sciences, the improvement of human health and the training of future generations of researchers. Jonas Salk, M.D., whose polio vaccine all but eradicated the crippling disease poliomyelitis in 1955, opened the Institute in 1965 with a gift of land from the City of San Diego and the financial support of the March of Dimes.
Mauricio Minotta | Newswise Science News
First time-lapse footage of cell activity during limb regeneration
25.10.2016 | eLife
Phenotype at the push of a button
25.10.2016 | Institut für Pflanzenbiochemie
Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.
This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...
Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion
Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.
"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
26.10.2016 | Power and Electrical Engineering
26.10.2016 | Awards Funding
26.10.2016 | Power and Electrical Engineering