Interview with Professor Hiroyuki Nakano
 
The sea is a treasure chest of unexplored biological resources. Seaweed, in particular, is a marine organism that is extremely promising as a source of biological, medicinal and health-related substances. Let’s make use of the wisdom of those who make their living by the sea and develop ways to effectively use seaweed.
 
Focus on the unknown potentials of seaweed. Here we have the world’s most advanced research on algal lectins.
 
  One of Professor Kanji Hori’s most well-known pieces of research is ‘Search for Algal Lectins and Development of Technology for Utilization’. The reason for Professor Hori embarking on this research was that there were very few examples of seaweed protein use, and almost no research being conducted on algal lectins (‘lectin’ is the generic term used to refer to proteins that recognize and bind specifically to sugars that exist in cell surfaces, cytoplasm, or bodily fluids).

As Professor Hori states, “There are many different types of seaweed, and its components are being used in various different ways, including food products, animal feed and fertilizer. Carbohydrates from seaweed are used as Japanese gelatin, alginic acid and fucoidan, for example, while its minerals are used as a supplemental source of iron and folic acid. Also, as a low-molecular weight compound, it is well known that the flavor component of seaweed broth is the amino acid monosodium glutamate, which is the base ingredient of Ajinomoto seasoning.
 
However, at the time there were very few examples of utilization of proteins which is one of the main constituents, and almost no research being conducted on algal lectins in particular. In the process of extracting protein from seaweed, the substance hardens when highly viscous polysaccharide components such as Japanese gelatin are present, making extraction problematic. This was one of the factors holding back research on seaweed proteins. After that time changes were made to the extraction process, and it is now possible to refine large amounts of lectin proteins.” Here are some of the figures that represent a part of the research results.

To date around 400 different types of algae have been screened, and it is said that around 240 varieties, or 60% of that amount, contain lectin. Professor Hori has identified a total of 64 lectin isolates (= refined), and characterized the primary structure of 27 lectins, the tertiary structure of 3 lectins (through joint research), and the genetic structure of 50 lectins. According to Professor Hori, “This is the only place in the world with such a large number of algal lectins”. Further, by investigating in detail the glycosylation and bioactivity properties of lectins, he has identified the features of algal lectins – in other words, their application characteristics.
 
What do the characteristics of algal lectins reveal? What are your future research goals?
 
The algal lectin characteristics that Professor Hori has identified so far may be broadly divided into three categories: 1. the novelty of carbohydrate recognition, 2. the novelty of their molecular structure, and 3. the diversity of their bioactivity. 

The first refers to the fact that algal lectins have extremely highly selective and high affinity binding with specific carbohydrate structures. “Sugars are attached to over 50% of proteins in mammals, and these sugars play a very important role. The sugar structure of the glycoproteins can be broadly divided into compound type, high-mannose type, and mixed sugar chains. The algal lectins recognize this sugar chain structure and select specific sugar chains and forcibly attach themselves to them. In particular, we have found that there are around 30 specific lectins that attach to high-mannose chains. We now know from the difference in the recognition site and the primary structure that they can be classified into four different types.”		  
 
The second point refers to the fact that most algal lectins are monomers with low molecular weight. They have an amino acid sequence that differs from known proteins, and that they form new lectin groups that show strong heat resistance.

Point 3 refers to the fact that we have discovered their diverse bioactivity, such as agglutination and lymphocyte mitogenic promotion of various cells, tumor cell proliferation, antivirus, antibacterial, platelet aggregation inhibition, anticoagulant, antiangiogenesis, associativity with food poisoning bacteria, and others.

“What these characteristics mean is that we can anticipate that they can be applied for use in biochemistry, clinical and ecosystem reagents, or as constituents in medications or functional foods. We are already moving ahead with some joint research together with professors in medical and science faculties of various universities and also other research institutions, and in the future I would like to proactively work on joint development projects with companies. Our research is focused on applications, studying things that can be useful in some way. This is why we are aiming to have our research results applied widely and used practically in various different fields,” says Professor Hori.
 
How will algal lectins be used in daily life considering future application possibilities?
 
  "Let’s take a look at some of the more concrete applications for algal lectins.

The first one is the development of an algal lectin chip to be used to identify carbohydrate structures. This searches for and prepares a large variety of algal lectins with different recognized carbohydrate structures, and uses those with a certain fixed surface area as sensors.

The second application is their development as clinical diagnosis medication. This would enable early diagnosis as a reagent used in the detection of bacterial species markers and disease markers.
 
The third application is development as a biochemical reagent. Investigating an extremely effective method of simple purification of chicken monoclonal antibodies whose purification was problematic (patent granted).
The fourth application is development as a medicinal constituent. For example, use as an antiviral agent (HIV-1, influenza virus, etc.) or anticancer agent. This is the application currently attracting the most attention, as it would prevent infection and become a carrier for a delivery system to take medication to the cancer cells alone.

The fifth application is development as a health food ingredient. Through oral administration, algal lectins have been found to be effective in the prevention of the onset of early-stage colon cancer.

The sixth application is development of useful seaweed culturing technology. This is also effective for the development of resources and environmental preservation. The possibilities should continue to expand in the future. We will continue with our research.”
 

Some examples of edible seaweed containing effective lectins
 
Kanji Hori
Professor, Marine Bioresource Chemistry
Hiroshima University Graduate School

Completed the doctoral program at Tokyo University Graduate School of Agriculture, 1976
Professor, Hiroshima University, April 1, 2000 –

Retired on March 31, 2015