Dr. Max D. Summers is a Distinguished Professor and Holder
of the Endowed Chair, in Agricultural Biotechnology at Texas A&M University.
He received an A.B. degree in biology in 1962 from Wilmington College
and a PhD in entomology from Purdue University in 1968. Summers was an
assistant and an associate professor of botany at the University of Texas
before moving to Texas A&M as a professor of entomology.
He is a member of the National Academy of Sciences, a Fellow in the American
Academy of Microbiology and a Fellow of the American Association for the
Advancement of Science. He was president of the American Society for Virology,
chair of Class VI of the National Academy of Sciences. The Houston Intellectual
Property Law Association honored him in 1999 as Inventor of the Year.
He has authored or co-authored more than 150 publications and was listed
in the top 250 (in the world) Most Highly Cited Authors in Microbiology
by the Institute for Scientific Information. He is also a member of the
Entomological Society of American Foundation Board of Councilors, and
the Texas Academy of Sciences, Engineering and Medicine.
Dr. Summers was the editor of Virology, and executive editor of Protein
Expression and Purification. He was a Foundation for Microbiology Lecturer
of the American Society for Microbiology. He received the first Distinguished
Alumni Award from the Purdue University School of Agriculture in 1992.
He has served on the U.S. Department of Commerce Biotechnology Technical
Advisory Committee, the National Academy of Sciences Council of the Government-University-Industry
Research Roundtable, and the Chiron Corporation Biotechnology Research
Award Nominating Committee. He was a panelist of the Accountability and
Federally Funded Research Panel, a sub committee of the Committee on Science,
Engineering and Public Policy on Government Performance and Results Act.
Research
contributions:
Baculovirus
Expression Vector System
Dr. Max D. Summers’ research emphasis is molecular biology of virion
maturation in the nucleus of cells. At the time the Baculovirus Expression
Vector System (BEVS) was developed, bacterial and yeast expression vectors
were available and both had demonstrated success with a number of proteins.
However, both of these systems had significant shortcomings when they
were used to produce structurally complex, biologically active proteins.
Thus, there was a compelling need to augment the existing expression systems
with a system that could produce proteins with properties more like those
produced in mammalian cells. The need dictated the development of a system
that would consistently produce proteins with authentic biological activity
with relative ease, at low cost, and at a scale that would allow protein
purification and detailed analysis.
As is often the case in biology, an alternative approach was developed
to solve this problem from research that was distant from the mainstream
approaches being used to develop expression vectors. While Max Summers
and his graduate student Gale Smith, were working on the molecular biology
of the family of insect viruses, Baculoviridae, they recognized that one
gene was expressed at extremely high levels. They initiated studies to
understand the essential elements of the promoter and the locus within
the viral genome. These studies resulted in the knowledge that the gene
was non-essential, and the strength of the promoter could be exploited
for foreign gene expression. As part of the early assessments of safety
for the baculoviruses, they also knew that this virus was non-toxic, did
not replicate in mammalian cells and that the design and development of
such an insect virus based vector system would have significant safety
advantages over other vector systems. He and Gale proceeded to use these
insights to develop the BEVS.
The Baculovirus Expression Vector System: The BEVS provides efficient,
low cost, large-scale production of functionally active proteins. It fills
many of the needs dictated by modern biological research. To date, well
over a thousand proteins have been expressed using the BEVS, with 98%
reported as biologically active. The BEVS then represents a breakthrough
technology that is facilitating current high-throughput proteomic studies.
The current explosion of knowledge of genomes and by extension the entire
protein complement of an organism, is allowing the development of a series
of new experimental tools. These are designed to facilitate understanding
of biological systems at an unprecedented rate. One of these tools is
the cloning of every gene encoded by an organism into a series of base
vectors that can be purchased by scientists for rapid experimental development.
The BEVS vectors are one of a small group of vectors that are being used
for the development of these tools.
The ability to generate large quantities of functionally authentic proteins
has opened many possible avenues for biological research. One such example
is demonstrated with membrane proteins, many of which are receptors and
primary targets for disease and modern medical intervention strategies.
If a normal cell has one hundred copies of a protein receptor residing
on the cell surface, it is not unusual for insect cell with a copy of
the BEVS expressed gene, to have 5,000 to 20,000 copies of functional
protein residing at the surface. This now facilitates the ability to assay
its’ activity and make comparison of function after exposure to
a spectrum of possible intervention agents. The BEVS is also being used
to produce protein for three-dimensional structure analysis. Such knowledge
provides for the precise design of intervention agents. The ability to
use BEVS as a source for protein crystals, and large-scale drug testing,
make the BEVS an important tool for drug discovery.
Another advantage of the BEVS is that the system not only can accept large
genes, but more than one gene can be expressed. In this manner, proteins
known to work in complexes can simultaneously be expressed to generate
active, functional complexes. The ability to simultaneously express multiple
genes has resulted in the understanding of complex structures. One example
is the ability to generate secreted and active recombinant antibodies
using BEVS. A second example has additional implications for the use of
BEVS. All of the structural proteins of bluetongue virus have been simultaneously
expressed using BEVS and this expression results in correctly assembled
capsids. A similar result has also been generated using BEVS to assemble
empty capsids of herpes simplex virus. Six viral genes assemble to generate
a herpes virus capsid, and by using viruses containing all or combinations
of these genes, the essential features of capsid formation was determined.
These studies not only revealed basic biology of virus structure and assembly,
but by removing the associated viral RNA or DNA, a system is developed
that shows great potential to produce safe and clean vaccines.
The potential of BEVS to rapidly develop a candidate human vaccine has
already been demonstrated. The Hong Kong ‘bird-flu’ virus
(HSN1) developed the ability to spread directly from chickens to human.
The virus was so deadly to chickens that the Hong Kong chicken industry
was devastated with mass poultry eliminations. Farm workers and those
involved in intervention programs were placed at significant risk of contracting
the disease. To assure the safety of the workers, NIH requested the development
of a vaccine. Protein Sciences, a company specializing in the use of the
BEVS technology, delivered 1700 doses of an experimental vaccine within
eight weeks. This included the time to identify, sequence and clone the
gene responsible for the flu symptoms. The vaccine was a success. Only
in science fiction can a vaccine be developed faster.
The BEVS represents a core technology that has greatly facilitated the
understanding of many proteins from many organisms. These studies have
broad applications and impact in basic research and practical medical
applications for both humans and animals. The importance and broad acceptance
of the BEVS technology is reflected in its acceptance in both the academic
community and private sector. The broad recognition and acceptance by
the scientific community is reflected in the determination by The Institute
of Scientific Information (ISI) that Dr. Summers is one of the top 250
most highly cited microbiologists in the world. Acceptance of the BEVS
by the private sector is reflected by the commercial licenses worldwide
that are held for the BEVS technology (currently >70). Thousands of
laboratories currently use the BEVS technology in their research programs.
The BEVS represents a core technology that has greatly facilitated the
understanding of many proteins from many organisms. These studies have
broad applications and impact in basic research and practical medical
applications for both humans and animals.
Sorting
of Integral Membrane Proteins to Nuclear Membranes Our research addresses the mechanism(s) of integral membrane
protein sorting and trafficking to the eukaryote cell inner nuclear membrane,
and to viral-induced intranuclear membranes. This is important because
mutations in a number of inner nuclear membrane proteins correlate with
several human diseases including muscular and lipid dystrophies. In eukaryotes,
the nucleus is delimited by the nuclear envelope (NE), which consists
of an outer nuclear membrane (ONM) and an inner nuclear membrane (INM)
separated by a lumen, and penetrated by nuclear pore complexes. The current
model for protein sorting to the INM states that integral proteins diffuse
between the continuous membrane of the endoplasmic reticulum (ER) and
the membranes of the NE, and are selectively retained at the INM by binding
with nuclear factors such as protein or DNA.
We study the sorting of baculovirus envelope proteins that transit from
their site of insertion in the ER, to the ONM and INM. These finally target
to viral induced vesicle precursors which to form in the nucleoplasm and
become the viral envelope. To identify potential regulatory and/or sorting
factors that function during viral infection, several virus envelope proteins
were studied for interactions with translocon proteins during integration.
We show by comparing photocrosslinking of viral and INM cellular proteins
through the translocon, that both viral and cellular transmembrane sequences
(TMSs) occupy a similar location in the translocon, yet occupy different
sites than do non-INM directed TMSs. These results provide evidence that:
1) INM directed TMSs are initially recognized and sorted at the translocon
(a proposed new role for ER translocons); and, 2) for some integral membrane
proteins, sorting to the nucleus may be an active process involving specific
non-nuclear proteins [Saksena et al. (2004) PNAS 101:12537].
Our studies also demonstrate that sorting of a viral envelope protein
to the INM is mediated by a specific INM-sorting motif (INM-SM). The INM-SM
consists of the 33 N-terminal amino acids which contain a TMS and associated
charges resulting in a specific orientation within the membrane [Braunagel
et al. (2004) PNAS 1001:8372-8377]. Using site-specific crosslinking it
was demonstrated following ER membrane integration, that the INM-SM is
adjacent to two viral proteins; and the deletion of one of these proteins
results in inefficient sorting of an integral membrane viral protein to
nuclear membranes. With the observation that viral proteins may specifically
facilitate viral envelope protein sorting to nuclear membranes, we speculate
that in normal cells specific cellular proteins may function to facilitate
sorting and trafficking. Using similar crosslinking experiments with the
same INM-SM integration intermediates, we are testing for INM-SM proximity
to cellular proteins that may facilitate the sorting of integral proteins
in transit to the INM. Our studies now provide evidence that the co-translational
integration and sorting of viral envelope proteins is a protein-facilitated
and protein-regulated multistep process which may also be utilized during
sorting of cellular INM directed proteins. Check our 2004 publications
for details.
