Refactor data tranfer object and model
This is very close to what AutoMapper is for. Though it doesn't directly support bidirectional maps, so you'll have to write a simple class that builds two mappers at the same time:

public class TwoWayMapper&lt;TSource, TDestination&gt;
{
    private readonly IMappingExpression&lt;TSource, TDestination&gt; m_sourceMapping =
        Mapper.CreateMap&lt;TSource, TDestination&gt;();
    private readonly IMappingExpression&lt;TDestination, TSource&gt; m_destinationMapping =
        Mapper.CreateMap&lt;TDestination, TSource&gt;();

    public TwoWayMapper&lt;TSource, TDestination&gt; ForMember(
        Expression&lt;Func&lt;TSource, object&gt;&gt; sourceMember,
        Expression&lt;Func&lt;TDestination, object&gt;&gt; destinationMember)
    {
        m_sourceMapping.ForMember(destinationMember, opt =&gt; opt.MapFrom(sourceMember));
        m_destinationMapping.ForMember(sourceMember, opt =&gt; opt.MapFrom(destinationMember));
        return this;
    }
}


You can then set up your mapping like this (maybe in a static constructor of ProjectOwnerDataFields?):

new TwoWayMapper&lt;ProjectOwnerDataFields, T_PROJECT&gt;()
    .ForMember(f =&gt; f.Id, p =&gt; p.proj_owner_id)
    .ForMember(f =&gt; f.CompanyName, p =&gt; p.proj_owner)
    .ForMember(f =&gt; f.ContactPerson, p =&gt; p.proj_owner_contact)
    .ForMember(f =&gt; f.CountryIsoLetter, p =&gt; p.proj_owner_country);
    // etc.


With that, your methods simplify to:

public ProjectOwnerDataFields(T_PROJECT project)
{
    Mapper.Map(project, this);
}

public void UpdateToModel(T_PROJECT project)
{
    Mapper.Map(this, project);
}